1/*
2 * Written by J.T. Conklin <jtc@netbsd.org>.
3 * Adapted for use as log2 by Ulrich Drepper <drepper@cygnus.com>.
4 * Public domain.
5 *
6 * Changed to use fyl2xp1 for values near 1, <drepper@cygnus.com>.
7 * Adapted for x86-64 by Andreas Jaeger <aj@suse.de>.
8 */
9
10#include <machine/asm.h>
11
12 .section .rodata.cst8,"aM",@progbits,8
13
14 .p2align 3
15 .type one,@object
16one: .double 1.0
17 ASM_SIZE_DIRECTIVE(one)
18 /* It is not important that this constant is precise. It is only
19 a value which is known to be on the safe side for using the
20 fyl2xp1 instruction. */
21 .type limit,@object
22limit: .double 0.29
23 ASM_SIZE_DIRECTIVE(limit)
24
25
26#ifdef PIC
27# define MO(op) op##(%rip)
28#else
29# define MO(op) op
30#endif
31
32 .text
33ENTRY(__ieee754_log2l)
34 fldl MO(one)
35 fldt 8(%rsp) // x : 1
36 fxam
37 fnstsw
38 fld %st // x : x : 1
39 testb $1, %ah
40 jnz 3f // in case x is NaN or ħInf
414: fsub %st(2), %st // x-1 : x : 1
42 fld %st // x-1 : x-1 : x : 1
43 fabs // |x-1| : x-1 : x : 1
44 fcompl MO(limit) // x-1 : x : 1
45 fnstsw // x-1 : x : 1
46 andb $0x45, %ah
47 jz 2f
48 fxam
49 fnstsw
50 andb $0x45, %ah
51 cmpb $0x40, %ah
52 jne 5f
53 fabs // log2(1) is +0 in all rounding modes.
545: fstp %st(1) // x-1 : 1
55 fyl2xp1 // log(x)
56 ret
57
582: fstp %st(0) // x : 1
59 fyl2x // log(x)
60 ret
61
623: testb $4, %ah
63 jnz 4b // in case x is ħInf
64 fstp %st(1)
65 fstp %st(1)
66 ret
67END (__ieee754_log2l)
68
69
70ENTRY(__log2l_finite)
71 fldl MO(one)
72 fldt 8(%rsp) // x : 1
73 fld %st // x : x : 1
74 fsub %st(2), %st // x-1 : x : 1
75 fld %st // x-1 : x-1 : x : 1
76 fabs // |x-1| : x-1 : x : 1
77 fcompl MO(limit) // x-1 : x : 1
78 fnstsw // x-1 : x : 1
79 andb $0x45, %ah
80 jz 2b
81 fxam
82 fnstsw
83 andb $0x45, %ah
84 cmpb $0x40, %ah
85 jne 6f
86 fabs // log2(1) is +0 in all rounding modes.
876: fstp %st(1) // x-1 : 1
88 fyl2xp1 // log(x)
89 ret
90END (__log2l_finite)
91