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authorRich Felker <dalias@aerifal.cx>2012-03-19 21:55:53 -0400
committerRich Felker <dalias@aerifal.cx>2012-03-19 21:55:53 -0400
commitacb744921b73f5a73803e533e5e4a4896d164a26 (patch)
tree2cdfcd2dc29d4d3041af99958215871ae5c900b6 /src/math
parent01084202815fefbb7db23825d8b11a570c455e13 (diff)
downloadmusl-acb744921b73f5a73803e533e5e4a4896d164a26.tar.gz
fix exp asm
exponents (base 2) near 16383 were broken due to (1) wrong cutoff, and (2) inability to fit the necessary range of scalings into a long double value. as a solution, we fall back to using frndint/fscale for insanely large exponents, and also have to special-case infinities here to avoid inf-inf generating nan. thankfully the costly code never runs in normal usage cases.
Diffstat (limited to 'src/math')
-rw-r--r--src/math/i386/exp.s45
1 files changed, 22 insertions, 23 deletions
diff --git a/src/math/i386/exp.s b/src/math/i386/exp.s
index 76ab4d64..ca0de1d4 100644
--- a/src/math/i386/exp.s
+++ b/src/math/i386/exp.s
@@ -68,21 +68,19 @@ exp:
.type exp2,@function
exp2:
fldl 4(%esp)
-1: mov $0x47000000,%eax
- push %eax
+1: pushl $0x467ff000
flds (%esp)
- shl $7,%eax
- push %eax
- add %eax,%eax
+ xorl %eax,%eax
+ pushl $0x80000000
push %eax
fld %st(1)
fabs
fucom %st(1)
fnstsw
- sahf
- ja 2f
fstp %st(0)
fstp %st(0)
+ sahf
+ ja 2f
fld %st(0)
fistpl 8(%esp)
fildl 8(%esp)
@@ -99,22 +97,23 @@ exp2:
add $12,%esp
ret
-2: fstp %st(0)
- fstp %st(0)
- fsts 8(%esp)
- mov 8(%esp),%eax
- lea (%eax,%eax),%ecx
- cmp $0xff000000,%ecx
- ja 2f
+2: fld %st(0)
+ fstpt (%esp)
+ mov 9(%esp),%ah
+ and $0x7f,%ah
+ cmp $0x7f,%ah
+ jne 1f
+ decb 9(%esp)
fstp %st(0)
- xor %ecx,%ecx
- inc %ecx
- add %eax,%eax
- jc 1f
- mov $0x7ffe,%ecx
-1: mov %ecx,8(%esp)
fldt (%esp)
- fld %st(0)
- fmulp
-2: add $12,%esp
+1: fld %st(0)
+ frndint
+ fxch %st(1)
+ fsub %st(1)
+ f2xm1
+ fld1
+ faddp
+ fscale
+ fstp %st(1)
+ add $12,%esp
ret