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Diffstat (limited to 'src/math/x86_64/expl.s')
-rw-r--r--src/math/x86_64/expl.s36
1 files changed, 17 insertions, 19 deletions
diff --git a/src/math/x86_64/expl.s b/src/math/x86_64/expl.s
index 64c1c78e..740bc779 100644
--- a/src/math/x86_64/expl.s
+++ b/src/math/x86_64/expl.s
@@ -40,7 +40,7 @@ exp2l:
mov %eax,-20(%rsp)
xor %eax,%eax
mov %eax,-24(%rsp)
- flds -16(%rsp)
+ flds -16(%rsp) # 16380
fld %st(1)
fabs
fucom %st(1)
@@ -48,7 +48,8 @@ exp2l:
fstp %st(0)
fstp %st(0)
sahf
- ja 2f
+ ja 3f # |x| > 16380
+ jp 2f # x is nan (avoid invalid except in fistp)
fld %st(0)
fistpl -16(%rsp)
fildl -16(%rsp)
@@ -58,28 +59,25 @@ exp2l:
add %eax,-16(%rsp)
f2xm1
fld1
- faddp
- fldt -24(%rsp)
+ faddp # 2^(x-rint(x))
+ fldt -24(%rsp) # 2^rint(x)
fmulp
- fstp %st(1)
+2: fstp %st(1)
ret
-2: fld %st(0)
+3: fld %st(0)
fstpt -24(%rsp)
- mov -15(%rsp),%ah
- and $0x7f,%ah
- cmp $0x7f,%ah
- jne 1f
- decb -15(%rsp)
- fstp %st(0)
- fldt -24(%rsp)
-1: fld %st(0)
+ fld1
+ mov -15(%rsp),%ax
+ and $0x7fff,%ax
+ cmp $0x7fff,%ax
+ je 1f # x = +-inf
+ fld %st(1)
frndint
- fxch %st(1)
- fsub %st(1)
+ fxch %st(2)
+ fsub %st(2) # st(0)=x-rint(x), st(1)=1, st(2)=rint(x)
f2xm1
- fld1
- faddp
- fscale
+ faddp # 2^(x-rint(x))
+1: fscale
fstp %st(1)
ret