From 04117dc8d44dde789d64f717c5d293a81316ad3d Mon Sep 17 00:00:00 2001 From: Jacek Caban Date: Mon, 8 Jun 2020 18:12:37 +0200 Subject: [PATCH] ntdll: Reimplement _allmul using 32-bit arithmetic. Based on compiler-rt. Signed-off-by: Jacek Caban Signed-off-by: Alexandre Julliard --- dlls/ntdll/large_int.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/dlls/ntdll/large_int.c b/dlls/ntdll/large_int.c index 7114b8c2d9d..cf8a3df0939 100644 --- a/dlls/ntdll/large_int.c +++ b/dlls/ntdll/large_int.c @@ -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; }