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math: fix x86_64 and x32 asm not to use sahf instruction 

Some early x86_64 cpus (released before 2006) did not support sahf/lahf
instructions so they should be avoided (intel manual says they are only
supported if CPUID.80000001H:ECX.LAHF-SAHF[bit 0] = 1).

The workaround simplifies exp2l and expm1l because fucomip can be
used instead of the fucomp;fnstsw;sahf sequence copied from i386.

In fmodl and remainderl sahf is replaced by a simple bit test.
This commit is contained in:
Szabolcs Nagy 2014-11-05 21:40:29 +01:00
parent de2b9c21d9
commit a732e80d33
6 changed files with 14 additions and 28 deletions
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13
src/math/x32/exp2l.s
View File

@ -6,9 +6,7 @@ expm1l:
fmulp
movl $0xc2820000,-4(%esp)
flds -4(%esp)
fucomp %st(1)
fnstsw %ax
sahf
fucomip %st(1)
fld1
jb 1f
# x*log2e <= -65, return -1 without underflow
@ -17,11 +15,8 @@ expm1l:
ret
1: fld %st(1)
fabs
fucom %st(1)
fnstsw %ax
fucomip %st(1)
fstp %st(0)
fstp %st(0)
sahf
ja 1f
f2xm1
ret
@ -53,9 +48,7 @@ exp2l:
fld %st(1)
fsub %st(1)
faddp
fucomp %st(1)
fnstsw
sahf
fucomip %st(1)
je 2f # x - 0x1p63 + 0x1p63 == x
movl $1,(%esp)
flds (%esp) # 0x1p-149

4
src/math/x32/fmodl.s
View File

@ -5,7 +5,7 @@ fmodl:
fldt 8(%esp)
1: fprem
fstsw %ax
sahf
jp 1b
testb $4,%ah
jnz 1b
fstp %st(1)
ret

4
src/math/x32/remainderl.s
View File

@ -5,7 +5,7 @@ remainderl:
fldt 8(%esp)
1: fprem1
fstsw %ax
sahf
jp 1b
testb $4,%ah
jnz 1b
fstp %st(1)
ret

13
src/math/x86_64/exp2l.s
View File

@ -6,9 +6,7 @@ expm1l:
fmulp
movl $0xc2820000,-4(%rsp)
flds -4(%rsp)
fucomp %st(1)
fnstsw %ax
sahf
fucomip %st(1)
fld1
jb 1f
# x*log2e <= -65, return -1 without underflow
@ -17,11 +15,8 @@ expm1l:
ret
1: fld %st(1)
fabs
fucom %st(1)
fnstsw %ax
fucomip %st(1)
fstp %st(0)
fstp %st(0)
sahf
ja 1f
f2xm1
ret
@ -53,9 +48,7 @@ exp2l:
fld %st(1)
fsub %st(1)
faddp
fucomp %st(1)
fnstsw
sahf
fucomip %st(1)
je 2f # x - 0x1p63 + 0x1p63 == x
movl $1,(%rsp)
flds (%rsp) # 0x1p-149

4
src/math/x86_64/fmodl.s
View File

@ -5,7 +5,7 @@ fmodl:
fldt 8(%rsp)
1: fprem
fstsw %ax
sahf
jp 1b
testb $4,%ah
jnz 1b
fstp %st(1)
ret

4
src/math/x86_64/remainderl.s
View File

@ -5,7 +5,7 @@ remainderl:
fldt 8(%rsp)
1: fprem1
fstsw %ax
sahf
jp 1b
testb $4,%ah
jnz 1b
fstp %st(1)
ret