2 * Written by J.T. Conklin <jtc@netbsd.org>.
3 * Adapted for use as log2 by Ulrich Drepper <drepper@cygnus.com>.
6 * Changed to use fyl2xp1 for values near 1, <drepper@cygnus.com>.
7 * Adapted for x86-64 by Andreas Jaeger <aj@suse.de>.
10 #include <machine/asm.h>
18 ASM_TYPE_DIRECTIVE(one,@object)
20 ASM_SIZE_DIRECTIVE(one)
21 /* It is not important that this constant is precise. It is only
22 a value which is known to be on the safe side for using the
23 fyl2xp1 instruction. */
24 ASM_TYPE_DIRECTIVE(limit,@object)
26 ASM_SIZE_DIRECTIVE(limit)
30 #define MO(op) op##(%rip)
36 ENTRY(__ieee754_log2l)
43 jnz 3f // in case x is NaN or ±Inf
44 4: fsub %st(2), %st // x-1 : x : 1
45 fld %st // x-1 : x-1 : x : 1
46 fabs // |x-1| : x-1 : x : 1
47 fcompl MO(limit) // x-1 : x : 1
51 fstp %st(1) // x-1 : 1
55 2: fstp %st(0) // x : 1
60 jnz 4b // in case x is ±Inf