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ntdll: Reimplement _allmul using 32-bit arithmetic. 

Based on compiler-rt.

Signed-off-by: Jacek Caban <jacek@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>
This commit is contained in:
Jacek Caban 2020-06-08 18:12:37 +02:00 committed by Alexandre Julliard
parent 0547da64a3
commit 04117dc8d4
1 changed files with 23 additions and 1 deletions
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24
dlls/ntdll/large_int.c
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@ -759,7 +759,29 @@ LONGLONG WINAPI _alldiv( LONGLONG a, LONGLONG b )
*/
LONGLONG WINAPI _allmul( LONGLONG a, LONGLONG b )
{
return a * b;
LARGE_INTEGER x = { .QuadPart = a };
LARGE_INTEGER y = { .QuadPart = b };
LARGE_INTEGER r;
unsigned int t;
const int bits_in_word_2 = 16;
const unsigned int lower_mask = ~0u >> bits_in_word_2;
r.u.LowPart = (x.u.LowPart & lower_mask) * (y.u.LowPart & lower_mask);
t = r.u.LowPart >> bits_in_word_2;
r.u.LowPart &= lower_mask;
t += (x.u.LowPart >> bits_in_word_2) * (y.u.LowPart & lower_mask);
r.u.LowPart += (t & lower_mask) << bits_in_word_2;
r.u.HighPart = t >> bits_in_word_2;
t = r.u.LowPart >> bits_in_word_2;
r.u.LowPart &= lower_mask;
t += (y.u.LowPart >> bits_in_word_2) * (x.u.LowPart & lower_mask);
r.u.LowPart += (t & lower_mask) << bits_in_word_2;
r.u.HighPart += t >> bits_in_word_2;
r.u.HighPart += (x.u.LowPart >> bits_in_word_2) * (y.u.LowPart >> bits_in_word_2);
r.u.HighPart += x.u.HighPart * y.u.LowPart + x.u.LowPart * y.u.HighPart;
return r.QuadPart;
}