optimize exponential asm for i386

up to 30% faster exp2 by avoiding slow frndint and fscale functions.
expm1 also takes a much more direct path for small arguments (the
expected usage case).

diff --git a/src/math/i386/exp.s b/src/math/i386/exp.s
index f4769d5..76ab4d6 100644 (file)
--- a/src/math/i386/exp.s
+++ b/src/math/i386/exp.s
@@ -1,3 +1,37 @@
+.global expm1f
+.type expm1f,@function
+expm1f:
+       flds 4(%esp)
+       jmp 1f
+
+.global expm1l
+.type expm1l,@function
+expm1l:
+       fldt 4(%esp)
+       jmp 1f
+
+.global expm1
+.type expm1,@function
+expm1:
+       fldl 4(%esp)
+1:     fldl2e
+       fmulp
+       fld1
+       fld %st(1)
+       fabs
+       fucom %st(1)
+       fnstsw %ax
+       fstp %st(0)
+       fstp %st(0)
+       sahf
+       ja 1f
+       f2xm1
+       ret
+1:     call 1f
+       fld1
+       fsubrp
+       ret
+

 .global exp2f
 .type exp2f,@function
 exp2f:
 .global exp2f
 .type exp2f,@function
 exp2f:


@@ -34,22 +68,53 @@ exp:
 .type exp2,@function
 exp2:
        fldl 4(%esp)
 .type exp2,@function
 exp2:
        fldl 4(%esp)

-1:     fxam
-       fnstsw %ax
+1:     mov $0x47000000,%eax
+       push %eax
+       flds (%esp)
+       shl $7,%eax
+       push %eax
+       add %eax,%eax
+       push %eax
+       fld %st(1)
+       fabs
+       fucom %st(1)
+       fnstsw

        sahf
        sahf

-       jnp 1f
-       jnc 1f
-       fstps 4(%esp)
-       mov $0xfe,%al
-       and %al,7(%esp)
-       flds 4(%esp)
-1:     fld %st(0)
-       frndint
+       ja 2f
+       fstp %st(0)
+       fstp %st(0)
+       fld %st(0)
+       fistpl 8(%esp)
+       fildl 8(%esp)

        fxch %st(1)
        fsub %st(1)
        fxch %st(1)
        fsub %st(1)

+       mov $0x3fff,%eax
+       add %eax,8(%esp)

        f2xm1
        fld1
        faddp
        f2xm1
        fld1
        faddp

-       fscale
+       fldt (%esp)
+       fmulp

        fstp %st(1)
        fstp %st(1)

+       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
+       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

        ret
        ret

diff --git a/src/math/i386/expm1.s b/src/math/i386/expm1.s
index bbb5d12..f335a3e 100644 (file)
--- a/src/math/i386/expm1.s
+++ b/src/math/i386/expm1.s
@@ -1,47 +1 @@
-.global expm1f
-.type expm1f,@function
-expm1f:
-       flds 4(%esp)
-       jmp 1f
-
-.global expm1l
-.type expm1l,@function
-expm1l:
-       fldt 4(%esp)
-       jmp 1f
-
-.global expm1
-.type expm1,@function
-expm1:
-       fldl 4(%esp)
-1:     fxam
-       fnstsw %ax
-       sahf
-       jnp 1f
-       jnc 1f
-       fstps 4(%esp)
-       mov $0xfe,%al
-       and %al,7(%esp)
-       flds 4(%esp)
-1:     fldl2e
-       fmulp
-       fld %st(0)
-       frndint
-       fldz
-       fcomp
-       fnstsw %ax
-       sahf
-       jnz 1f
-       fstp %st(0)
-       f2xm1
-       ret
-1:     fxch %st(1)
-       fsub %st(1)
-       f2xm1
-       fld1
-       faddp
-       fscale
-       fld1
-       fsubrp
-       fstp %st(1)
-       ret
+# see exp.s