OpenLibm/i387/e_exp.S

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/*
* Written by:
* J.T. Conklin (jtc@netbsd.org)
* Public domain.
*/
#include <i387/bsd_asm.h>
/* e^x = 2^(x * log2(e)) */
ENTRY(exp)
/*
* If x is +-Inf, then the subtraction would give Inf-Inf = NaN.
* Avoid this. Also avoid it if x is NaN for convenience.
*/
movl 8(%esp),%eax
andl $0x7fffffff,%eax
cmpl $0x7ff00000,%eax
jae x_Inf_or_NaN
fldl 4(%esp)
/*
* Extended precision is needed to reduce the maximum error from
* hundreds of ulps to less than 1 ulp. Switch to it if necessary.
* We may as well set the rounding mode to to-nearest and mask traps
* if we switch.
*/
fstcw 4(%esp)
movl 4(%esp),%eax
andl $0x0300,%eax
cmpl $0x0300,%eax /* RC == 0 && PC == 3? */
je 1f /* jump if mode is good */
movl $0x137f,8(%esp)
fldcw 8(%esp)
1:
fldl2e
fmulp /* x * log2(e) */
fst %st(1)
frndint /* int(x * log2(e)) */
fst %st(2)
fsubrp /* fract(x * log2(e)) */
f2xm1 /* 2^(fract(x * log2(e))) - 1 */
fld1
faddp /* 2^(fract(x * log2(e))) */
fscale /* e^x */
fstp %st(1)
je 1f
fldcw 4(%esp)
1:
ret
x_Inf_or_NaN:
/*
* Return 0 if x is -Inf. Otherwise just return x; when x is Inf
* this gives Inf, and when x is a NaN this gives the same result
* as (x + x) (x quieted).
*/
cmpl $0xfff00000,8(%esp)
jne x_not_minus_Inf
cmpl $0,4(%esp)
jne x_not_minus_Inf
fldz
ret
x_not_minus_Inf:
fldl 4(%esp)
ret
END(exp)
//
/* Enable stack protection */
#if defined(__ELF__)
.section .note.GNU-stack,"",%progbits
#endif