52 lines
1.1 KiB
ArmAsm
52 lines
1.1 KiB
ArmAsm
/*
|
|
* 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>.
|
|
*
|
|
* Removed header file dependency for use in libmingwex.a by
|
|
* Danny Smith <dannysmith@users.sourceforge.net>
|
|
*/
|
|
|
|
.file "log2f.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 _log2f
|
|
.def _log2f; .scl 2; .type 32; .endef
|
|
_log2f:
|
|
fldl one
|
|
flds 4(%esp) // x : 1
|
|
fxam
|
|
fnstsw
|
|
fld %st // x : x : 1
|
|
sahf
|
|
jc 3f // in case x is NaN or ±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 ±Inf
|
|
fstp %st(1)
|
|
fstp %st(1)
|
|
ret
|