c - 关于整数格式转换

Question

来自英特尔的 article :

The integer format conversions are commonly used in imaging and video applications. For example, they can be used when converting RGBA from four bytes to four floats prior to computation on a pixel. One SSE4 convert instruction can do the same thing as four SIMD instructions did previously, as shown.

SSE2: 
pmovd xmm0, m32 
pxor xmm7, xmm7 
punpcklbw xmm0, xmm7 
punpcklwd xmm0, xmm7 
cvtdq2ps xmm0, xmm0

SSE4: 
pmovzxbd xmm0, m32 
cvtdq2ps xmm0, xmm0

有人可以给我看一个完整的例子吗？非常感谢!

Answer 1

因为 pmovzxbd 仅适用于 32 位内存操作数或 128 位 sse 寄存器，而不适用于通用寄存器，您需要插入一些类型转换或从 GPR 到 SSE 的显式加载。

__m128 convert_RGBA_to_float(float* rgba) {
    return  _mm_cvtepi32_ps( _mm_cvtepu8_epi32 ( *(__m128i*)rgba) );
}