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target-i386: implement lzcnt emulation

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lzcnt is a AMD Phenom/Barcelona added instruction returning the
number of leading zero bits in a word.
As this is similar to the "bsr" instruction, reuse the existing
code. There need to be some more changes, though, as lzcnt always
returns a valid value (in opposite to bsr, which has a special
case when the operand is 0).
lzcnt is guarded by the ABM CPUID bit (Fn8000_0001:ECX_5).

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Andre Przywara 2009-10-23 13:44:31 +02:00 • committed by Aurelien Jarno
parent cb2dbfc351
commit 31501a714b
3 changed files with 38 additions and 14 deletions
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14
target-i386/op_helper.c
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@ -5479,11 +5479,14 @@ target_ulong helper_bsf(target_ulong t0)
return count;
}
target_ulong helper_bsr(target_ulong t0)
target_ulong helper_lzcnt(target_ulong t0, int wordsize)
{
int count;
target_ulong res, mask;
if (wordsize > 0 && t0 == 0) {
return wordsize;
}
res = t0;
count = TARGET_LONG_BITS - 1;
mask = (target_ulong)1 << (TARGET_LONG_BITS - 1);
@ -5491,9 +5494,16 @@ target_ulong helper_bsr(target_ulong t0)
count--;
res <<= 1;
}
if (wordsize > 0) {
return wordsize - 1 - count;
}
return count;
}
target_ulong helper_bsr(target_ulong t0)
{
return helper_lzcnt(t0, 0);
}
static int compute_all_eflags(void)
{