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0 pointsdbaupp10y ago0 comments

Aren't numeric promotions only applied in mixed expressions? (However, I'm not a C language-lawyer, so I could very easily be incorrect.)

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4 comments · 2 top-level

aidenn010y ago· 2 in thread

All smaller than int types are promoted to int before calculations are done. I was wrong that uint32_t is smaller than int though.

For an actual example:

  uint32_t combineTwoUint16(uint16_t x, uint16_t y)
  {
    return x<<16 | y;
  }

If int is larger than 16 bits, then this is technically undefined behavior in the case that x is greater than 2^15 as it's signed integer overflow.

vtsrh10y ago

Well the solution is simple:

  return (x+0U)<<16 | (y+0U);

Would it be insane to have a inline library for every arithmetic operation, that would handle such cases and offer addition optional functionality?

lmm10y ago

The intersection of people who are willing to rewrite all their arithmetic to use such a library with people who are not willing to switch to a non-C language is rather small.

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pcwalton10y ago

No, sadly. In some cases (floating point) what happens is even implementation-dependent (though queryable with FLT_EVAL_METHOD).

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