c - 将 2 个带符号的短裤存储在一个无符号整数中

Question

这是给定的:

signed short a, b;
a = -16;
b = 340;

现在我想将这 2 条签名短裤存储在一个 unsigned int 中，稍后再次检索这 2 条签名短裤。我尝试了这个，但生成的短裤不一样:

unsigned int c = a << 16 | b;

signed short ar, br;
ar = c >> 16;
br = c & 0xFFFF;

Answer 1

OP 几乎是对的

#include <assert.h>
#include <limits.h>

unsigned ab_to_c(signed short a, signed short b) {
  assert(SHRT_MAX == 32767);
  assert(UINT_MAX == 4294967295);
  // unsigned int c = a << 16 | b; fails as `b` get sign extended before the `|`.
  // *1u insures the shift of `a` is done as `unsigned` to avoid UB 
  //    of shifting into the sign bit.
  unsigned c = (a*1u << 16) | (b & 0xFFFF);
  return c;
}

void c_to_ab(unsigned c, signed short *a, signed short *b) {
  *a = c >> 16;
  *b = c & 0xFFFF;
}