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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>.
*/
#include <machine/asm.h>
.section .rodata.cst8,"aM",@progbits,8
.p2align 3
.type one,@object
one: .double 1.0
ASM_SIZE_DIRECTIVE(one)
/* 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. */
.type limit,@object
limit: .double 0.29
ASM_SIZE_DIRECTIVE(limit)
#ifdef PIC
# define MO(op) op##@GOTOFF(%edx)
#else
# define MO(op) op
#endif
.text
ENTRY(__ieee754_log2)
#ifdef PIC
LOAD_PIC_REG (dx)
#endif
fldl MO(one)
fldl 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 MO(limit) // x-1 : x : 1
fnstsw // x-1 : x : 1
andb $0x45, %ah
jz 2f
fxam
fnstsw
andb $0x45, %ah
cmpb $0x40, %ah
jne 5f
fabs // log2(1) is +0 in all rounding modes.
5: 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
END (__ieee754_log2)
strong_alias (__ieee754_log2, __log2_finite)
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