"Ronald S. Bultje" <rsbul...@gmail.com> writes:
> Hi,
>
> 2011/4/7 Benjamin Larsson <ba...@ludd.ltu.se>:
>> +static inline int32_t mul32(int32_t a, int32_t b)
>> +{
>> + /* on >=i686, gcc compiles this into a single "imull" instruction */
>> + int64_t r = (int64_t)a * b;
>> + /* round the result before truncating - improves accuracy */
>> + return (r + 0x80000000) >> 32;
>> +}
>
> I believe this is what the MUL64() macro is for, then it works on
> non-x86 archs also, but that doesn't round...
ARM has a rounding version of that instruction FWIW.
--
Måns Rullgård
m...@mansr.com
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