newlib/winsup/mingw/mingwex/math/log2l.S

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/*
* Written by J.T. Conklin <jtc@netbsd.org>.
* Adapted for use as log2 by Ulrich Drepper <drepper@cygnus.com>.
* Public domain.
*
* Changed to use fyl2xp1 for values near 1, <drepper@cygnus.com>.
*/
.file "log2l.S"
.text
.align 4
one: .double 1.0
/* It is not important that this constant is precise. It is only
a value which is known to be on the safe side for using the
fyl2xp1 instruction. */
limit: .double 0.29
.text
.align 4
.globl _log2l
.def _log2l; .scl 2; .type 32; .endef
_log2l:
fldl one
fldt 4(%esp) // x : 1
fxam
fnstsw
fld %st // x : x : 1
sahf
jc 3f // in case x is NaN or <EFBFBD>Inf
4: fsub %st(2), %st // x-1 : x : 1
fld %st // x-1 : x-1 : x : 1
fabs // |x-1| : x-1 : x : 1
fcompl limit // x-1 : x : 1
fnstsw // x-1 : x : 1
andb $0x45, %ah
jz 2f
fstp %st(1) // x-1 : 1
fyl2xp1 // log(x)
ret
2: fstp %st(0) // x : 1
fyl2x // log(x)
ret
3: jp 4b // in case x is <EFBFBD>Inf
fstp %st(1)
fstp %st(1)
ret