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 */ 8 9#include <machine/asm.h> 10 11#ifdef __ELF__ 12 .section .rodata 13#else 14 .text 15#endif 16 .align ALIGNARG(4) 17 ASM_TYPE_DIRECTIVE(one,@object) 18one: .double 1.0 19 ASM_SIZE_DIRECTIVE(one) 20 /* It is not important that this constant is precise. It is only 21 a value which is known to be on the safe side for using the 22 fyl2xp1 instruction. */ 23 ASM_TYPE_DIRECTIVE(limit,@object) 24limit: .double 0.29 25 ASM_SIZE_DIRECTIVE(limit) 26 27 28#ifdef PIC 29#define MO(op) op##@GOTOFF(%edx) 30#else 31#define MO(op) op 32#endif 33 34 .text 35ENTRY(__ieee754_log2f) 36#ifdef PIC 37 call 1f 381: popl %edx 39 addl $_GLOBAL_OFFSET_TABLE_+[.-1b], %edx 40#endif 41 fldl MO(one) 42 flds 4(%esp) // x : 1 43 fxam 44 fnstsw 45 fld %st // x : x : 1 46 sahf 47 jc 3f // in case x is NaN or �Inf 484: fsub %st(2), %st // x-1 : x : 1 49 fld %st // x-1 : x-1 : x : 1 50 fabs // |x-1| : x-1 : x : 1 51 fcompl MO(limit) // x-1 : x : 1 52 fnstsw // x-1 : x : 1 53 andb $0x45, %ah 54 jz 2f 55 fstp %st(1) // x-1 : 1 56 fyl2xp1 // log(x) 57 ret 58 592: fstp %st(0) // x : 1 60 fyl2x // log(x) 61 ret 62 633: jp 4b // in case x is �Inf 64 fstp %st(1) 65 fstp %st(1) 66 ret 67END (__ieee754_log2f) 68