c++ - 在内联汇编中访问 thread

c++ - 在内联汇编中访问 thread_local 变量

转载作者：太空狗更新时间：2023-10-29 20:07:59

我正在处理一些具有使用内联汇编的优化版本的 C++ 代码。
优化版本表现出的行为不是线程安全的，这可以追溯到 3 个从程序集内部广泛访问的全局变量。

__attribute__ ((aligned (16))) unsigned int SHAVITE_MESS[16];
__attribute__ ((aligned (16))) thread_local unsigned char SHAVITE_PTXT[8*4];
__attribute__ ((aligned (16))) unsigned int SHAVITE_CNTS[4] = {0,0,0,0};

...

asm ("movaps xmm0, SHAVITE_PTXT[rip]");
asm ("movaps xmm1, SHAVITE_PTXT[rip+16]");
asm ("movaps xmm3, SHAVITE_CNTS[rip]");
asm ("movaps xmm4, SHAVITE256_XOR2[rip]");
asm ("pxor   xmm2,  xmm2");

我天真地认为解决这个问题的最简单方法是使变量成为thread_local，但是这会导致程序集中的段错误 - 看起来程序集不知道变量是线程本地的？

我在一个小的 thread_local 测试用例的汇编中挖掘了一些，看看 gcc 如何处理它们 mov eax, DWORD PTR fs:num1@tpoff 并尝试修改代码以执行相同的操作:

asm ("movaps xmm0, fs:SHAVITE_PTXT@tpoff");
asm ("movaps xmm1, fs:SHAVITE_PTXT@tpoff+16");
asm ("movaps xmm3, fs:SHAVITE_CNTS@tpoff");
asm ("movaps xmm4, fs:SHAVITE256_XOR2@tpoff");
asm ("pxor   xmm2,  xmm2");

如果所有变量也是thread_local，它也可以工作，它也与引用实现(非程序集)匹配，因此似乎可以成功工作。
然而，这似乎是特定于 CPU 的，如果我查看使用 -m32 编译的输出，我会得到 mov eax, DWORD PTR gs:num1@ntpoff
由于代码无论如何都是“x86”特定的(使用 aes-ni)，我想我可以简单地反编译并实现所有可能的变体。

然而，我并不真正喜欢将其作为解决方案，感觉有点像猜测编程。进一步这样做并不能真正帮助我为将来的任何此类案例学习任何东西，这些案例可能不太特定于一种架构。

有没有更通用/正确的方法来处理这个问题？
我如何以更通用的方式告诉程序集变量是 thread_local？
或者有没有一种方法可以传递变量，这样它就不需要知道并且无论如何都可以工作？

最佳答案

正如另一个答案所说，内联汇编是一团糟并且被滥用了。 用内在函数重写应该是好的 ，并允许您使用或不使用 -mavx(或 -march=haswell 或 -march=znver1 或其他)进行编译，让编译器保存一堆寄存器复制指令。

它还允许编译器优化( vector )寄存器分配以及何时加载/存储，这是编译器非常擅长的。

好吧，我无法使用您提供的测试数据。它使用了这里没有提供的其他几个例程，我懒得去找它们。

也就是说，我能够为测试数据拼凑一些东西。我的 E256() 返回与您相同的值。这并不意味着我 100% 正确(您需要自己进行测试)，但是考虑到所有异或/aesenc 一遍又一遍地针对所有内容，如果出现问题，我希望它表演。

转换为内在函数并不是特别困难。大多数情况下，您只需要为给定的 asm 指令 找到等效的 _mm_ 函数。当你的意思是 x13 (grrr).

请注意，虽然此代码使用名为 x0-x15 的变量，但这只是因为它使翻译更容易。这些 C 变量名称与 gcc 在编译代码时将使用的寄存器之间没有相关性。此外，gcc 使用了大量有关 SSE 的知识来重新排序指令，因此输出(尤其是 -O3)与原始 asm 非常不同。如果您认为可以比较它们以检查正确性(就像我所做的那样)，那么您可能会感到沮丧。

此代码包含原始例程(以“old”为前缀)和新例程，并从 main() 调用两者以查看它们是否产生相同的输出。我没有努力对内置函数进行任何更改以尝试对其进行优化。一旦它起作用，我就停下来了。我会把任何进一步的改进留给你，因为它都是 C 代码。

也就是说，gcc 能够优化内在函数(它不能为 asm 做这件事)。这意味着如果您使用 -mavx2 重新编译此代码，生成的代码将大不相同。

一些统计数据:

E256() 的原始(完全扩展)代码占用了 287 条指令。

使用不带 -mavx2 的内在函数构建需要 251。

使用 -mavx2 构建内部函数需要 196。

我没有做过任何计时，但我相信删除大约 100 行 asm 会有所帮助。 OTOH，有时 gcc 在优化 SSE 方面做得很糟糕，所以不要假设任何事情。

希望这可以帮助。

// Compile with -O3 -msse4.2 -maes
//           or -O3 -msse4.2 -maes -mavx2
#include <wmmintrin.h>
#include <x86intrin.h>
#include <stdio.h>

///////////////////////////
#define tos(a) #a
#define tostr(a) tos(a)

#define rev_reg_0321(j){ asm ("pshufb xmm" tostr(j)", [oldSHAVITE_REVERSE]"); }

#define replace_aes(i, j){ asm ("aesenc xmm" tostr(i)", xmm" tostr(j)""); }

__attribute__ ((aligned (16))) unsigned int oldSHAVITE_MESS[16];
__attribute__ ((aligned (16))) unsigned char oldSHAVITE_PTXT[8*4];
__attribute__ ((aligned (16))) unsigned int oldSHAVITE_CNTS[4] = {0,0,0,0};
__attribute__ ((aligned (16))) unsigned int oldSHAVITE_REVERSE[4] = {0x07060504, 0x0b0a0908, 0x0f0e0d0c, 0x03020100 };
__attribute__ ((aligned (16))) unsigned int oldSHAVITE256_XOR2[4] = {0x0, 0xFFFFFFFF, 0x0, 0x0};
__attribute__ ((aligned (16))) unsigned int oldSHAVITE256_XOR3[4] = {0x0, 0x0, 0xFFFFFFFF, 0x0};
__attribute__ ((aligned (16))) unsigned int oldSHAVITE256_XOR4[4] = {0x0, 0x0, 0x0, 0xFFFFFFFF};

#define oldmixing() do {\
    asm("movaps xmm11, xmm15");\
    asm("movaps xmm10, xmm14");\
    asm("movaps xmm9, xmm13");\
    asm("movaps xmm8, xmm12");\
\
    asm("movaps xmm6, xmm11");\
    asm("psrldq xmm6, 4");\
    asm("pxor xmm8, xmm6");\
    asm("movaps xmm6, xmm8");\
    asm("pslldq xmm6, 12");\
    asm("pxor xmm8, xmm6");\
\
    asm("movaps xmm7, xmm8");\
    asm("psrldq xmm7, 4");\
    asm("pxor xmm9, xmm7");\
    asm("movaps xmm7, xmm9");\
    asm("pslldq xmm7, 12");\
    asm("pxor xmm9, xmm7");\
\
    asm("movaps xmm6, xmm9");\
    asm("psrldq xmm6, 4");\
    asm("pxor xmm10, xmm6");\
    asm("movaps xmm6, xmm10");\
    asm("pslldq xmm6, 12");\
    asm("pxor xmm10, xmm6");\
\
    asm("movaps xmm7, xmm10");\
    asm("psrldq xmm7, 4");\
    asm("pxor xmm11, xmm7");\
    asm("movaps xmm7, xmm11");\
    asm("pslldq xmm7, 12");\
    asm("pxor xmm11, xmm7");\
} while(0);

void oldE256()
{
    asm (".intel_syntax noprefix");

    /* (L,R) = (xmm0,xmm1) */
    asm ("movaps xmm0, [oldSHAVITE_PTXT]");
    asm ("movaps xmm1, [oldSHAVITE_PTXT+16]");
    asm ("movaps xmm3, [oldSHAVITE_CNTS]");
    asm ("movaps xmm4, [oldSHAVITE256_XOR2]");
    asm ("pxor xmm2, xmm2");

    /* init key schedule */
    asm ("movaps xmm8, [oldSHAVITE_MESS]");
    asm ("movaps xmm9, [oldSHAVITE_MESS+16]");
    asm ("movaps xmm10, [oldSHAVITE_MESS+32]");
    asm ("movaps xmm11, [oldSHAVITE_MESS+48]");

    /* xmm8..xmm11 = rk[0..15] */

    /* start key schedule */
    asm ("movaps xmm12, xmm8");
    asm ("movaps xmm13, xmm9");
    asm ("movaps xmm14, xmm10");
    asm ("movaps xmm15, xmm11");

    rev_reg_0321(12);
    rev_reg_0321(13);
    rev_reg_0321(14);
    rev_reg_0321(15);
    replace_aes(12, 2);
    replace_aes(13, 2);
    replace_aes(14, 2);
    replace_aes(15, 2);

    asm ("pxor xmm12, xmm3");
    asm ("pxor xmm12, xmm4");
    asm ("movaps xmm4, [oldSHAVITE256_XOR3]");
    asm ("pxor xmm12, xmm11");
    asm ("pxor xmm13, xmm12");
    asm ("pxor xmm14, xmm13");
    asm ("pxor xmm15, xmm14");
    /* xmm12..xmm15 = rk[16..31] */

    /* F3 - first round */

    asm ("movaps xmm6, xmm8");
    asm ("pxor xmm8, xmm1");
    replace_aes(8, 9);
    replace_aes(8, 10);
    replace_aes(8, 2);
    asm ("pxor xmm0, xmm8");
    asm ("movaps xmm8, xmm6");

    /* F3 - second round */

    asm ("movaps xmm6, xmm11");
    asm ("pxor xmm11, xmm0");
    replace_aes(11, 12);
    replace_aes(11, 13);
    replace_aes(11, 2);
    asm ("pxor xmm1, xmm11");
    asm ("movaps xmm11, xmm6");

    /* key schedule */
    oldmixing();

    /* xmm8..xmm11 - rk[32..47] */

    /* F3 - third round */
    asm ("movaps xmm6, xmm14");
    asm ("pxor xmm14, xmm1");
    replace_aes(14, 15);
    replace_aes(14, 8);
    replace_aes(14, 2);
    asm ("pxor xmm0, xmm14");
    asm ("movaps xmm14, xmm6");

    /* key schedule */

    asm ("pshufd xmm3, xmm3,135");

    asm ("movaps xmm12, xmm8");
    asm ("movaps xmm13, xmm9");
    asm ("movaps xmm14, xmm10");
    asm ("movaps xmm15, xmm11");
    rev_reg_0321(12);
    rev_reg_0321(13);
    rev_reg_0321(14);
    rev_reg_0321(15);
    replace_aes(12, 2);
    replace_aes(13, 2);
    replace_aes(14, 2);
    replace_aes(15, 2);

    asm ("pxor xmm12, xmm11");
    asm ("pxor xmm14, xmm3");
    asm ("pxor xmm14, xmm4");
    asm ("movaps xmm4, [oldSHAVITE256_XOR4]");
    asm ("pxor xmm13, xmm12");
    asm ("pxor xmm14, xmm13");
    asm ("pxor xmm15, xmm14");

    /* xmm12..xmm15 - rk[48..63] */

    /* F3 - fourth round */
    asm ("movaps xmm6, xmm9");
    asm ("pxor xmm9, xmm0");
    replace_aes(9, 10);
    replace_aes(9, 11);
    replace_aes(9, 2);
    asm ("pxor xmm1, xmm9");
    asm ("movaps xmm9, xmm6");

    /* key schedule */
    oldmixing();
    /* xmm8..xmm11 = rk[64..79] */

    /* F3 - fifth round */
    asm ("movaps xmm6, xmm12");
    asm ("pxor xmm12, xmm1");
    replace_aes(12, 13);
    replace_aes(12, 14);
    replace_aes(12, 2);
    asm ("pxor xmm0, xmm12");
    asm ("movaps xmm12, xmm6");

    /* F3 - sixth round */
    asm ("movaps xmm6, xmm15");
    asm ("pxor xmm15, xmm0");
    replace_aes(15, 8);
    replace_aes(15, 9);
    replace_aes(15, 2);
    asm ("pxor xmm1, xmm15");
    asm ("movaps xmm15, xmm6");

    /* key schedule */
    asm ("pshufd xmm3, xmm3, 147");

    asm ("movaps xmm12, xmm8");
    asm ("movaps xmm13, xmm9");
    asm ("movaps xmm14, xmm10");
    asm ("movaps xmm15, xmm11");
    rev_reg_0321(12);
    rev_reg_0321(13);
    rev_reg_0321(14);
    rev_reg_0321(15);
    replace_aes(12, 2);
    replace_aes(13, 2);
    replace_aes(14, 2);
    replace_aes(15, 2);
    asm ("pxor xmm12, xmm11");
    asm ("pxor xmm13, xmm3");
    asm ("pxor xmm13, xmm4");
    asm ("pxor xmm13, xmm12");
    asm ("pxor xmm14, xmm13");
    asm ("pxor xmm15, xmm14");

    /* xmm12..xmm15 = rk[80..95] */

    /* F3 - seventh round */
    asm ("movaps xmm6, xmm10");
    asm ("pxor xmm10, xmm1");
    replace_aes(10, 11);
    replace_aes(10, 12);
    replace_aes(10, 2);
    asm ("pxor xmm0, xmm10");
    asm ("movaps xmm10, xmm6");

    /* key schedule */
    oldmixing();

    /* xmm8..xmm11 = rk[96..111] */

    /* F3 - eigth round */
    asm ("movaps xmm6, xmm13");
    asm ("pxor xmm13, xmm0");
    replace_aes(13, 14);
    replace_aes(13, 15);
    replace_aes(13, 2);
    asm ("pxor xmm1, xmm13");
    asm ("movaps xmm13, xmm6");

    /* key schedule */
    asm ("pshufd xmm3, xmm3, 135");

    asm ("movaps xmm12, xmm8");
    asm ("movaps xmm13, xmm9");
    asm ("movaps xmm14, xmm10");
    asm ("movaps xmm15, xmm11");
    rev_reg_0321(12);
    rev_reg_0321(13);
    rev_reg_0321(14);
    rev_reg_0321(15);
    replace_aes(12, 2);
    replace_aes(13, 2);
    replace_aes(14, 2);
    replace_aes(15, 2);
    asm ("pxor xmm12, xmm11");
    asm ("pxor xmm15, xmm3");
    asm ("pxor xmm15, xmm4");
    asm ("pxor xmm13, xmm12");
    asm ("pxor xmm14, xmm13");
    asm ("pxor xmm15, xmm14");

    /* xmm12..xmm15 = rk[112..127] */

    /* F3 - ninth round */
    asm ("movaps xmm6, xmm8");
    asm ("pxor xmm8, xmm1");
    replace_aes(8, 9);
    replace_aes(8, 10);
    replace_aes(8, 2);
    asm ("pxor xmm0, xmm8");
    asm ("movaps xmm8, xmm6");
    /* F3 - tenth round */
    asm ("movaps xmm6, xmm11");
    asm ("pxor xmm11, xmm0");
    replace_aes(11, 12);
    replace_aes(11, 13);
    replace_aes(11, 2);
    asm ("pxor xmm1, xmm11");
    asm ("movaps xmm11, xmm6");

    /* key schedule */
    oldmixing();

    /* xmm8..xmm11 = rk[128..143] */

    /* F3 - eleventh round */
    asm ("movaps xmm6, xmm14");
    asm ("pxor xmm14, xmm1");
    replace_aes(14, 15);
    replace_aes(14, 8);
    replace_aes(14, 2);
    asm ("pxor xmm0, xmm14");
    asm ("movaps xmm14, xmm6");

    /* F3 - twelfth round */
    asm ("movaps xmm6, xmm9");
    asm ("pxor xmm9, xmm0");
    replace_aes(9, 10);
    replace_aes(9, 11);
    replace_aes(9, 2);
    asm ("pxor xmm1, xmm9");
    asm ("movaps xmm9, xmm6");

    /* feedforward */
    asm ("pxor xmm0, [oldSHAVITE_PTXT]");
    asm ("pxor xmm1, [oldSHAVITE_PTXT+16]");
    asm ("movaps [oldSHAVITE_PTXT], xmm0");
    asm ("movaps [oldSHAVITE_PTXT+16], xmm1");
    asm (".att_syntax noprefix");

    return;
}

void oldCompress256(const unsigned char *message_block, unsigned char *chaining_value, unsigned long long counter,
    const unsigned char salt[32])
{
    int i, j;

    for (i=0;i<8*4;i++)
        oldSHAVITE_PTXT[i]=chaining_value[i];

     for (i=0;i<16;i++)
        oldSHAVITE_MESS[i] = *((unsigned int*)(message_block+4*i));

    oldSHAVITE_CNTS[0] = (unsigned int)(counter & 0xFFFFFFFFULL);
    oldSHAVITE_CNTS[1] = (unsigned int)(counter>>32);
    /* encryption + Davies-Meyer transform */
    oldE256();

    for (i=0; i<4*8; i++)
        chaining_value[i]=oldSHAVITE_PTXT[i];

     return;
}

////////////////////////////////

__attribute__ ((aligned (16))) unsigned int SHAVITE_MESS[16];
__attribute__ ((aligned (16))) unsigned char SHAVITE_PTXT[8*4];
__attribute__ ((aligned (16))) unsigned int SHAVITE_CNTS[4] = {0,0,0,0};
__attribute__ ((aligned (16))) unsigned int SHAVITE_REVERSE[4] = {0x07060504, 0x0b0a0908, 0x0f0e0d0c, 0x03020100 };
__attribute__ ((aligned (16))) unsigned int SHAVITE256_XOR2[4] = {0x0, 0xFFFFFFFF, 0x0, 0x0};
__attribute__ ((aligned (16))) unsigned int SHAVITE256_XOR3[4] = {0x0, 0x0, 0xFFFFFFFF, 0x0};
__attribute__ ((aligned (16))) unsigned int SHAVITE256_XOR4[4] = {0x0, 0x0, 0x0, 0xFFFFFFFF};

#define mixing() do {\
    x11 = x15; \
    x10 = x14; \
    x9 = x13;\
    x8 = x12;\
\
    x6 = x11;\
    x6 = _mm_srli_si128(x6, 4);\
    x8 = _mm_xor_si128(x8, x6);\
    x6 = x8;\
    x6 = _mm_slli_si128(x6, 12);\
    x8 = _mm_xor_si128(x8, x6);\
\
    x7 = x8;\
    x7 = _mm_srli_si128(x7, 4);\
    x9 = _mm_xor_si128(x9, x7);\
    x7 = x9;\
    x7 = _mm_slli_si128(x7, 12);\
    x9 = _mm_xor_si128(x9, x7);\
\
    x6 = x9;\
    x6 = _mm_srli_si128(x6, 4);\
    x10 = _mm_xor_si128(x10, x6);\
    x6 = x10;\
    x6 = _mm_slli_si128(x6, 12);\
    x10 = _mm_xor_si128(x10, x6);\
\
    x7 = x10;\
    x7 = _mm_srli_si128(x7, 4);\
    x11 = _mm_xor_si128(x11, x7);\
    x7 = x11;\
    x7 = _mm_slli_si128(x7, 12);\
    x11 = _mm_xor_si128(x11, x7);\
} while(0);

void E256()
{
    __m128i x0;
    __m128i x1;
    __m128i x2;
    __m128i x3;
    __m128i x4;
    __m128i x5;
    __m128i x6;
    __m128i x7;
    __m128i x8;
    __m128i x9;
    __m128i x10;
    __m128i x11;
    __m128i x12;
    __m128i x13;
    __m128i x14;
    __m128i x15;

    /* (L,R) = (xmm0,xmm1) */
    const __m128i ptxt1 = _mm_loadu_si128((const __m128i*)SHAVITE_PTXT);
    const __m128i ptxt2 = _mm_loadu_si128((const __m128i*)(SHAVITE_PTXT+16));

    x0 = ptxt1;
    x1 = ptxt2;

    x3 = _mm_loadu_si128((__m128i*)SHAVITE_CNTS);
    x4 = _mm_loadu_si128((__m128i*)SHAVITE256_XOR2);
    x2 = _mm_setzero_si128();

    /* init key schedule */
    x8 = _mm_loadu_si128((__m128i*)SHAVITE_MESS);
    x9 = _mm_loadu_si128((__m128i*)(SHAVITE_MESS+4));
    x10 = _mm_loadu_si128((__m128i*)(SHAVITE_MESS+8));
    x11 = _mm_loadu_si128((__m128i*)(SHAVITE_MESS+12));

    /* xmm8..xmm11 = rk[0..15] */

    /* start key schedule */
    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;

const __m128i xtemp = _mm_loadu_si128((__m128i*)SHAVITE_REVERSE);
    x12 = _mm_shuffle_epi8(x12, xtemp);
    x13 = _mm_shuffle_epi8(x13, xtemp);
    x14 = _mm_shuffle_epi8(x14, xtemp);
    x15 = _mm_shuffle_epi8(x15, xtemp);

    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);

    x12 = _mm_xor_si128(x12, x3);
    x12 = _mm_xor_si128(x12, x4);
    x4 = _mm_loadu_si128((__m128i*)SHAVITE256_XOR3);
    x12 = _mm_xor_si128(x12, x11);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);
    /* xmm12..xmm15 = rk[16..31] */

    /* F3 - first round */

    x6 = x8;
    x8 = _mm_xor_si128(x8, x1);
    x8 = _mm_aesenc_si128(x8, x9);
    x8 = _mm_aesenc_si128(x8, x10);
    x8 = _mm_aesenc_si128(x8, x2);
    x0 = _mm_xor_si128(x0, x8);
    x8 = x6;

    /* F3 - second round */

    x6 = x11;
    x11 = _mm_xor_si128(x11, x0);
    x11 = _mm_aesenc_si128(x11, x12);
    x11 = _mm_aesenc_si128(x11, x13);
    x11 = _mm_aesenc_si128(x11, x2);
    x1 = _mm_xor_si128(x1, x11);
    x11 = x6;

    /* key schedule */
    mixing();

    /* xmm8..xmm11 - rk[32..47] */

    /* F3 - third round */
    x6 = x14;
    x14 = _mm_xor_si128(x14, x1);
    x14 = _mm_aesenc_si128(x14, x15);
    x14 = _mm_aesenc_si128(x14, x8);
    x14 = _mm_aesenc_si128(x14, x2);
    x0 = _mm_xor_si128(x0, x14);
    x14 = x6;

    /* key schedule */

    x3 = _mm_shuffle_epi32(x3, 135);

    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;
    x12 = _mm_shuffle_epi8(x12, xtemp);
    x13 = _mm_shuffle_epi8(x13, xtemp);
    x14 = _mm_shuffle_epi8(x14, xtemp);
    x15 = _mm_shuffle_epi8(x15, xtemp);
    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);

    x12 = _mm_xor_si128(x12, x11);
    x14 = _mm_xor_si128(x14, x3);
    x14 = _mm_xor_si128(x14, x4);
    x4 = _mm_loadu_si128((__m128i*)SHAVITE256_XOR4);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);

    /* xmm12..xmm15 - rk[48..63] */

    /* F3 - fourth round */
    x6 = x9;
    x9 = _mm_xor_si128(x9, x0);
    x9 = _mm_aesenc_si128(x9, x10);
    x9 = _mm_aesenc_si128(x9, x11);
    x9 = _mm_aesenc_si128(x9, x2);
    x1 = _mm_xor_si128(x1, x9);
    x9 = x6;

    /* key schedule */
    mixing();
    /* xmm8..xmm11 = rk[64..79] */

    /* F3 - fifth round */
    x6 = x12;
    x12 = _mm_xor_si128(x12, x1);
    x12 = _mm_aesenc_si128(x12, x13);
    x12 = _mm_aesenc_si128(x12, x14);
    x12 = _mm_aesenc_si128(x12, x2);
    x0 = _mm_xor_si128(x0, x12);
    x12 = x6;

    /* F3 - sixth round */
    x6 = x15;
    x15 = _mm_xor_si128(x15, x0);
    x15 = _mm_aesenc_si128(x15, x8);
    x15 = _mm_aesenc_si128(x15, x9);
    x15 = _mm_aesenc_si128(x15, x2);
    x1 = _mm_xor_si128(x1, x15);
    x15 = x6;

    /* key schedule */
    x3 = _mm_shuffle_epi32(x3, 147);

    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;
    x12 = _mm_shuffle_epi8(x12, xtemp);
    x13 = _mm_shuffle_epi8(x13, xtemp);
    x14 = _mm_shuffle_epi8(x14, xtemp);
    x15 = _mm_shuffle_epi8(x15, xtemp);
    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);
    x12 = _mm_xor_si128(x12, x11);
    x13 = _mm_xor_si128(x13, x3);
    x13 = _mm_xor_si128(x13, x4);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);

    /* xmm12..xmm15 = rk[80..95] */

    /* F3 - seventh round */
    x6 = x10;
    x10 = _mm_xor_si128(x10, x1);
    x10 = _mm_aesenc_si128(x10, x11);
    x10 = _mm_aesenc_si128(x10, x12);
    x10 = _mm_aesenc_si128(x10, x2);
    x0 = _mm_xor_si128(x0, x10);
    x10 = x6;

    /* key schedule */
    mixing();

    /* xmm8..xmm11 = rk[96..111] */

    /* F3 - eigth round */
    x6 = x13;
    x13 = _mm_xor_si128(x13, x0);
    x13 = _mm_aesenc_si128(x13, x14);
    x13 = _mm_aesenc_si128(x13, x15);
    x13 = _mm_aesenc_si128(x13, x2);
    x1 = _mm_xor_si128(x1, x13);
    x13 = x6;

    /* key schedule */
    x3 = _mm_shuffle_epi32(x3, 135);

    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;
    x12 = _mm_shuffle_epi8(x12, xtemp);
    x13 = _mm_shuffle_epi8(x13, xtemp);
    x14 = _mm_shuffle_epi8(x14, xtemp);
    x15 = _mm_shuffle_epi8(x15, xtemp);
    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);
    x12 = _mm_xor_si128(x12, x11);
    x15 = _mm_xor_si128(x15, x3);
    x15 = _mm_xor_si128(x15, x4);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);

    /* xmm12..xmm15 = rk[112..127] */

    /* F3 - ninth round */
    x6 = x8;
    x8 = _mm_xor_si128(x8, x1);
    x8 = _mm_aesenc_si128(x8, x9);
    x8 = _mm_aesenc_si128(x8, x10);
    x8 = _mm_aesenc_si128(x8, x2);
    x0 = _mm_xor_si128(x0, x8);
    x8 = x6;
    /* F3 - tenth round */
    x6 = x11;
    x11 = _mm_xor_si128(x11, x0);
    x11 = _mm_aesenc_si128(x11, x12);
    x11 = _mm_aesenc_si128(x11, x13);
    x11 = _mm_aesenc_si128(x11, x2);
    x1 = _mm_xor_si128(x1, x11);
    x11 = x6;

    /* key schedule */
    mixing();

    /* xmm8..xmm11 = rk[128..143] */

    /* F3 - eleventh round */
    x6 = x14;
    x14 = _mm_xor_si128(x14, x1);
    x14 = _mm_aesenc_si128(x14, x15);
    x14 = _mm_aesenc_si128(x14, x8);
    x14 = _mm_aesenc_si128(x14, x2);
    x0 = _mm_xor_si128(x0, x14);
    x14 = x6;

    /* F3 - twelfth round */
    x6 = x9;
    x9 = _mm_xor_si128(x9, x0);
    x9 = _mm_aesenc_si128(x9, x10);
    x9 = _mm_aesenc_si128(x9, x11);
    x9 = _mm_aesenc_si128(x9, x2);
    x1 = _mm_xor_si128(x1, x9);
    x9 = x6;

    /* feedforward */
    x0 = _mm_xor_si128(x0, ptxt1);
    x1 = _mm_xor_si128(x1, ptxt2);
    _mm_storeu_si128((__m128i *)SHAVITE_PTXT, x0);
    _mm_storeu_si128((__m128i *)(SHAVITE_PTXT + 16), x1);

    return;
}

void Compress256(const unsigned char *message_block, unsigned char *chaining_value, unsigned long long counter,
    const unsigned char salt[32])
{
    int i, j;

    for (i=0;i<8*4;i++)
        SHAVITE_PTXT[i]=chaining_value[i];

    for (i=0;i<16;i++)
        SHAVITE_MESS[i] = *((unsigned int*)(message_block+4*i));

    SHAVITE_CNTS[0] = (unsigned int)(counter & 0xFFFFFFFFULL);
    SHAVITE_CNTS[1] = (unsigned int)(counter>>32);
    /* encryption + Davies-Meyer transform */
    E256();

    for (i=0; i<4*8; i++)
        chaining_value[i]=SHAVITE_PTXT[i];

     return;
}

int main(int argc, char *argv[])
{
    const int cvlen = 32;
    unsigned char *cv = (unsigned char *)malloc(cvlen);

    for (int x=0; x < cvlen; x++)
        cv[x] = x + argc;

    const int mblen = 64;
    unsigned char *mb = (unsigned char *)malloc(mblen);

    for (int x=0; x < mblen; x++)
        mb[x] = x + argc;

    unsigned long long counter = 0x1234567812345678ull;

    unsigned char s[32] = {0};
    oldCompress256(mb, cv, counter, s);

    printf("old: ");
    for (int x=0; x < cvlen; x++)
        printf("%2x ", cv[x]);
    printf("\n");

    for (int x=0; x < cvlen; x++)
        cv[x] = x + argc;

    Compress256(mb, cv, counter, s);

    printf("new: ");
    for (int x=0; x < cvlen; x++)
        printf("%2x ", cv[x]);
    printf("\n");
}

编辑:

全局变量仅用于在 C 和 asm 之间传递值。也许 asm 编写者不知道如何访问参数？ IAC，它们是不必要的(也是线程安全问题的根源)。这是没有它们的代码(以及一些外观更改):

#include <x86intrin.h>
#include <stdio.h>
#include <time.h>

#define mixing() \
    x11 = x15;\
    x10 = x14;\
    x9 = x13;\
    x8 = x12;\
\
    x6 = x11;\
    x6 = _mm_srli_si128(x6, 4);\
    x8 = _mm_xor_si128(x8, x6);\
    x6 = x8;\
    x6 = _mm_slli_si128(x6, 12);\
    x8 = _mm_xor_si128(x8, x6);\
\
    x7 = x8;\
    x7 = _mm_srli_si128(x7, 4);\
    x9 = _mm_xor_si128(x9, x7);\
    x7 = x9;\
    x7 = _mm_slli_si128(x7, 12);\
    x9 = _mm_xor_si128(x9, x7);\
\
    x6 = x9;\
    x6 = _mm_srli_si128(x6, 4);\
    x10 = _mm_xor_si128(x10, x6);\
    x6 = x10;\
    x6 = _mm_slli_si128(x6, 12);\
    x10 = _mm_xor_si128(x10, x6);\
\
    x7 = x10;\
    x7 = _mm_srli_si128(x7, 4);\
    x11 = _mm_xor_si128(x11, x7);\
    x7 = x11;\
    x7 = _mm_slli_si128(x7, 12);\
    x11 = _mm_xor_si128(x11, x7);

// If mess & chain won't be 16byte aligned, change _mm_load to _mm_loadu and
// _mm_store to _mm_storeu
void Compress256(const __m128i *mess, __m128i *chain, unsigned long long counter, const unsigned char salt[32])
{
    // note: _mm_set_epi32 uses (int e3, int e2, int e1, int e0)
    const __m128i SHAVITE_REVERSE = _mm_set_epi32(0x03020100, 0x0f0e0d0c, 0x0b0a0908, 0x07060504);
    const __m128i SHAVITE256_XOR2 = _mm_set_epi32(0x0, 0x0, 0xFFFFFFFF, 0x0);
    const __m128i SHAVITE256_XOR3 = _mm_set_epi32(0x0, 0xFFFFFFFF, 0x0, 0x0);
    const __m128i SHAVITE256_XOR4 = _mm_set_epi32(0xFFFFFFFF, 0x0, 0x0, 0x0);
    const __m128i SHAVITE_CNTS =
        _mm_set_epi32(0, 0, (unsigned int)(counter>>32), (unsigned int)(counter & 0xFFFFFFFFULL));

    __m128i x0, x1, x2, x3, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;

    /* (L,R) = (xmm0,xmm1) */
    const __m128i ptxt1 = _mm_load_si128(chain);
    const __m128i ptxt2 = _mm_load_si128(chain+1);

    x0 = ptxt1;
    x1 = ptxt2;

    x3 = SHAVITE_CNTS;
    x2 = _mm_setzero_si128();

    /* init key schedule */
    x8 = _mm_load_si128(mess);
    x9 = _mm_load_si128(mess+1);
    x10 = _mm_load_si128(mess+2);
    x11 = _mm_load_si128(mess+3);

    /* xmm8..xmm11 = rk[0..15] */

    /* start key schedule */
    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;

    x12 = _mm_shuffle_epi8(x12, SHAVITE_REVERSE);
    x13 = _mm_shuffle_epi8(x13, SHAVITE_REVERSE);
    x14 = _mm_shuffle_epi8(x14, SHAVITE_REVERSE);
    x15 = _mm_shuffle_epi8(x15, SHAVITE_REVERSE);

    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);

    x12 = _mm_xor_si128(x12, x3);
    x12 = _mm_xor_si128(x12, SHAVITE256_XOR2);
    x12 = _mm_xor_si128(x12, x11);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);

    /* xmm12..xmm15 = rk[16..31] */

    /* F3 - first round */
    x6 = x8;
    x8 = _mm_xor_si128(x8, x1);
    x8 = _mm_aesenc_si128(x8, x9);
    x8 = _mm_aesenc_si128(x8, x10);
    x8 = _mm_aesenc_si128(x8, x2);
    x0 = _mm_xor_si128(x0, x8);
    x8 = x6;

    /* F3 - second round */
    x6 = x11;
    x11 = _mm_xor_si128(x11, x0);
    x11 = _mm_aesenc_si128(x11, x12);
    x11 = _mm_aesenc_si128(x11, x13);
    x11 = _mm_aesenc_si128(x11, x2);
    x1 = _mm_xor_si128(x1, x11);
    x11 = x6;

    /* key schedule */
    mixing();

    /* xmm8..xmm11 - rk[32..47] */

    /* F3 - third round */
    x6 = x14;
    x14 = _mm_xor_si128(x14, x1);
    x14 = _mm_aesenc_si128(x14, x15);
    x14 = _mm_aesenc_si128(x14, x8);
    x14 = _mm_aesenc_si128(x14, x2);
    x0 = _mm_xor_si128(x0, x14);
    x14 = x6;

    /* key schedule */
    x3 = _mm_shuffle_epi32(x3, 135);

    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;
    x12 = _mm_shuffle_epi8(x12, SHAVITE_REVERSE);
    x13 = _mm_shuffle_epi8(x13, SHAVITE_REVERSE);
    x14 = _mm_shuffle_epi8(x14, SHAVITE_REVERSE);
    x15 = _mm_shuffle_epi8(x15, SHAVITE_REVERSE);
    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);

    x12 = _mm_xor_si128(x12, x11);
    x14 = _mm_xor_si128(x14, x3);
    x14 = _mm_xor_si128(x14, SHAVITE256_XOR3);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);

    /* xmm12..xmm15 - rk[48..63] */

    /* F3 - fourth round */
    x6 = x9;
    x9 = _mm_xor_si128(x9, x0);
    x9 = _mm_aesenc_si128(x9, x10);
    x9 = _mm_aesenc_si128(x9, x11);
    x9 = _mm_aesenc_si128(x9, x2);
    x1 = _mm_xor_si128(x1, x9);
    x9 = x6;

    /* key schedule */
    mixing();

    /* xmm8..xmm11 = rk[64..79] */

    /* F3 - fifth round */
    x6 = x12;
    x12 = _mm_xor_si128(x12, x1);
    x12 = _mm_aesenc_si128(x12, x13);
    x12 = _mm_aesenc_si128(x12, x14);
    x12 = _mm_aesenc_si128(x12, x2);
    x0 = _mm_xor_si128(x0, x12);
    x12 = x6;

    /* F3 - sixth round */
    x6 = x15;
    x15 = _mm_xor_si128(x15, x0);
    x15 = _mm_aesenc_si128(x15, x8);
    x15 = _mm_aesenc_si128(x15, x9);
    x15 = _mm_aesenc_si128(x15, x2);
    x1 = _mm_xor_si128(x1, x15);
    x15 = x6;

    /* key schedule */
    x3 = _mm_shuffle_epi32(x3, 147);

    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;
    x12 = _mm_shuffle_epi8(x12, SHAVITE_REVERSE);
    x13 = _mm_shuffle_epi8(x13, SHAVITE_REVERSE);
    x14 = _mm_shuffle_epi8(x14, SHAVITE_REVERSE);
    x15 = _mm_shuffle_epi8(x15, SHAVITE_REVERSE);
    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);
    x12 = _mm_xor_si128(x12, x11);
    x13 = _mm_xor_si128(x13, x3);
    x13 = _mm_xor_si128(x13, SHAVITE256_XOR4);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);

    /* xmm12..xmm15 = rk[80..95] */

    /* F3 - seventh round */
    x6 = x10;
    x10 = _mm_xor_si128(x10, x1);
    x10 = _mm_aesenc_si128(x10, x11);
    x10 = _mm_aesenc_si128(x10, x12);
    x10 = _mm_aesenc_si128(x10, x2);
    x0 = _mm_xor_si128(x0, x10);
    x10 = x6;

    /* key schedule */
    mixing();

    /* xmm8..xmm11 = rk[96..111] */

    /* F3 - eigth round */
    x6 = x13;
    x13 = _mm_xor_si128(x13, x0);
    x13 = _mm_aesenc_si128(x13, x14);
    x13 = _mm_aesenc_si128(x13, x15);
    x13 = _mm_aesenc_si128(x13, x2);
    x1 = _mm_xor_si128(x1, x13);
    x13 = x6;

    /* key schedule */
    x3 = _mm_shuffle_epi32(x3, 135);

    x12 = x8;
    x13 = x9;
    x14 = x10;
    x15 = x11;
    x12 = _mm_shuffle_epi8(x12, SHAVITE_REVERSE);
    x13 = _mm_shuffle_epi8(x13, SHAVITE_REVERSE);
    x14 = _mm_shuffle_epi8(x14, SHAVITE_REVERSE);
    x15 = _mm_shuffle_epi8(x15, SHAVITE_REVERSE);
    x12 = _mm_aesenc_si128(x12, x2);
    x13 = _mm_aesenc_si128(x13, x2);
    x14 = _mm_aesenc_si128(x14, x2);
    x15 = _mm_aesenc_si128(x15, x2);
    x12 = _mm_xor_si128(x12, x11);
    x15 = _mm_xor_si128(x15, x3);
    x15 = _mm_xor_si128(x15, SHAVITE256_XOR4);
    x13 = _mm_xor_si128(x13, x12);
    x14 = _mm_xor_si128(x14, x13);
    x15 = _mm_xor_si128(x15, x14);

    /* xmm12..xmm15 = rk[112..127] */

    /* F3 - ninth round */
    x6 = x8;
    x8 = _mm_xor_si128(x8, x1);
    x8 = _mm_aesenc_si128(x8, x9);
    x8 = _mm_aesenc_si128(x8, x10);
    x8 = _mm_aesenc_si128(x8, x2);
    x0 = _mm_xor_si128(x0, x8);
    x8 = x6;

    /* F3 - tenth round */
    x6 = x11;
    x11 = _mm_xor_si128(x11, x0);
    x11 = _mm_aesenc_si128(x11, x12);
    x11 = _mm_aesenc_si128(x11, x13);
    x11 = _mm_aesenc_si128(x11, x2);
    x1 = _mm_xor_si128(x1, x11);
    x11 = x6;

    /* key schedule */
    mixing();

    /* xmm8..xmm11 = rk[128..143] */

    /* F3 - eleventh round */
    x6 = x14;
    x14 = _mm_xor_si128(x14, x1);
    x14 = _mm_aesenc_si128(x14, x15);
    x14 = _mm_aesenc_si128(x14, x8);
    x14 = _mm_aesenc_si128(x14, x2);
    x0 = _mm_xor_si128(x0, x14);
    x14 = x6;

    /* F3 - twelfth round */
    x6 = x9;
    x9 = _mm_xor_si128(x9, x0);
    x9 = _mm_aesenc_si128(x9, x10);
    x9 = _mm_aesenc_si128(x9, x11);
    x9 = _mm_aesenc_si128(x9, x2);
    x1 = _mm_xor_si128(x1, x9);
    x9 = x6;

    /* feedforward */
    x0 = _mm_xor_si128(x0, ptxt1);
    x1 = _mm_xor_si128(x1, ptxt2);
    _mm_store_si128(chain, x0);
    _mm_store_si128(chain + 1, x1);
}

int main(int argc, char *argv[])
{
    __m128i chain[2], mess[4];
    unsigned char *p;

    // argc prevents compiler from precalculating results

    p = (unsigned char *)mess;
    for (int x=0; x < 64; x++)
        p[x] = x + argc;

    p = (unsigned char *)chain;
    for (int x=0; x < 32; x++)
        p[x] = x + argc;

    unsigned long long counter = 0x1234567812345678ull + argc;

    // Unused, but prototype requires it.
    unsigned char s[32] = {0};

    Compress256(mess, chain, counter, s);

    for (int x=0; x < 32; x++)
        printf("%02x ", p[x]);
    printf("\n");

    struct timespec start, end;
    clock_gettime(CLOCK_MONOTONIC, &start);

    unsigned char res = 0;

    for (int x=0; x < 400000; x++)
    {
        Compress256(mess, chain, counter, s);

        // Ensure optimizer doesn't omit the calc
        res ^= *p;
    }
    clock_gettime(CLOCK_MONOTONIC, &end);

    unsigned long long delta_us = (end.tv_sec - start.tv_sec) * 1000000ull + (end.tv_nsec - start.tv_nsec) / 1000ull;
    printf("%x: %llu\n", res, delta_us);
}

关于c++ - 在内联汇编中访问 thread_local 变量，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/57664080/

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javascript if( 变量 = =(变量 2 || 变量 3 || ...))
这个问题在这里已经有了答案: 关闭 10 年前。 Possible Duplicate: How to nest OR statements in JavaScript? 有没有办法做到这一点:
JavaScript 变量 = 变量
在 JavaScript 中有没有办法让一个变量总是等于一个变量？喜欢var1 = var2但是当var2更新，也是var1 . 例子 var var1 = document.getElementBy
python - 如何阅读此 python 代码？变量 1 = 变量 2 == 变量 3
我正在努力理解这代表什么 var1 = var2 == var3 我的猜测是这等同于: if (var2 == var3): var1 = var2 最佳答案赋值 var1 = var2
php - 变量 $_GET 变量
这个问题已经有答案了: What does the PHP error message "Notice: Use of undefined constant" mean? (2 个回答) 已关闭 8
MySQL:变量=变量+select语句
我在临时表中有几条记录，我想从每条记录中获取一个值并将其添加到一个变量中，例如 color | caption -------------------------------- re
linux - 如何将原始字符串转换为变量(变量 --> $变量)？
如何将字符串转为变量(字符串变量--> $variable)？或者用逗号分隔的变量列表然后转换为实际变量。我有 2 个文件: 列名文件行文件我需要根据字符串匹配行文件中的整行，并根据列名文件命
PHP:来自与变量(变量-变量)连接的字符串的新变量
我有一个我无法解决的基本 php 问题，我也想了解为什么! $upperValueCB = 10; $passNodeMatrixSource = 'CB'; $topValue= '$uppe
php 变量 = 变量 1 ||变量2
这可能吗？ php $variable = $variable1 || $variable2? 如果 $variable1 为空则使用 $variable2 是否存在类似的东西？最佳答案 PHP 5
perl - for 循环不会修改 `my` 变量，但会修改 `our` 变量
在 Perl 5.20 中，for 循环似乎能够修改模块作用域的变量，但不能修改父作用域中的词法变量。 #!/usr/bin/env perl use strict; use warnings; ou
JavaScript: 变量 = 变量.concat(另一个变量);
为什么这不起作用: var variable; variable = variable.concat(variable2); $('#lunk').append(variable) 我无法弄清楚这一点
c++ - 指针的大小(*变量 VS 变量)
根据我的理解，在32位机器上，指针的sizeof是32位(4字节)，而在64位机器上，它是8字节。无论它们指向什么数据类型，它们都有固定的大小。我的计算机在 64 位上运行，但是当我打印包含 * 的大
java - 变量+=值和变量=变量+值之间的区别；
例如: int a = 10; a += 1.5; 这运行得很完美，但是 a = a+1.5; 此作业表示类型不匹配:无法从 double 转换为 int。所以我的问题是:+= 运算符和= 运算符
MySQL 语法错误 |变量 = 变量 + 整数
您好，我写了这个 MySQL 存储过程，但我一直收到这个语法错误 #1064 - You have an error in your SQL syntax; check the manual that
swift - 如果(变量 == 变量 + 5)
我试图在我的场景中显示特定的奖牌，这取决于你的高分是基于关卡的目标。 // Get Medal Colour if levelHighscore goalScore { sc
c++ - 变量 = !!变量与变量 =(变量!= 0)
我必须维护相当古老的 Visual C++ 源代码的大型代码库。我发现代码如下: bIsOk = !!m_ptr->isOpen(some Parameters) bIsOk的数据类型是bool，is
php - Javascript 变量，发送到 PHP 变量
我有一个从 MySQL 数据库中提取的动态产品列表。在 list 上有一个立即联系按钮，我正在使用一个 jquery Modal 脚本，它会弹出一个表单。我的问题是尝试将产品信息变量传递给该弹出窗
c++ - 类型(变量)与(类型)变量
这个问题在这里已经有了答案: 关闭 10 年前。 Possible Duplicate: What is the difference between (type)value and type(va
javascript - 变量 === 未定义与 typeof 变量 === "undefined"
jQuery Core Style Guidelines建议两种不同的方法来检查变量是否已定义。全局变量:typeof variable === "undefined" 局部变量:variable
jquery - 动态(变量)变量(如 php 中的？)
这个问题已经有答案了: 已关闭11 年前。 Possible Duplicate: “Variable” Variables in Javascript? 我想肯定有一种方法可以在 JavaScrip
c# - 变量 1 = 变量 2 = 真；优点缺点？
在语句中使用多重赋值有什么优点或缺点吗？在简单的例子中 var1 = var2 = true; 赋值是从右到左的(我相信 C# 中的所有赋值都是如此，而且可能是 Java，尽管我没有检查后者)。但是，

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c++ - 在内联汇编中访问 thread_local 变量