sysdeps/i386/fpu/e_log.S

   1 /*
   2  * Written by J.T. Conklin <jtc@netbsd.org>.
   3  * Public domain.
   4  *
   5  * Changed to use fyl2xp1 for values near 1, <drepper@cygnus.com>.
   6  */
   7
   8 #include <machine/asm.h>
   9
  10 RCSID("$NetBSD: e_log.S,v 1.4 1995/05/08 23:48:39 jtc Exp $")
  11
  12 #ifdef __ELF__
  13         .section .rodata
  14 #else
  15         .text
  16 #endif
  17         .align ALIGNARG(4)
  18         ASM_TYPE_DIRECTIVE(one,@object)
  19 one:    .double 1.0
  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)
  25 limit:  .double 0.29
  26         ASM_SIZE_DIRECTIVE(limit)
  27
  28
  29 #ifdef PIC
  30 #define MO(op) op##@GOTOFF(%edx)
  31 #else
  32 #define MO(op) op
  33 #endif
  34
  35         .text
  36 ENTRY(__ieee754_log)
  37         fldln2                  // log(2)
  38         fldl    4(%esp)         // x : log(2)
  39         fxam
  40         fnstsw
  41 #ifdef PIC
  42         LOAD_PIC_REG (dx)
  43 #endif
  44         fld     %st             // x : x : log(2)
  45         sahf
  46         jc      3f              // in case x is NaN or +-Inf
  47 4:      fsubl   MO(one)         // x-1 : x : log(2)
  48         fld     %st             // x-1 : x-1 : x : log(2)
  49         fabs                    // |x-1| : x-1 : x : log(2)
  50         fcompl  MO(limit)       // x-1 : x : log(2)
  51         fnstsw                  // x-1 : x : log(2)
  52         andb    $0x45, %ah
  53         jz      2f
  54         fstp    %st(1)          // x-1 : log(2)
  55         fyl2xp1                 // log(x)
  56         ret
  57
  58 2:      fstp    %st(0)          // x : log(2)
  59         fyl2x                   // log(x)
  60         ret
  61
  62 3:      jp      4b              // in case x is +-Inf
  63         fstp    %st(1)
  64         fstp    %st(1)
  65         ret
  66 END (__ieee754_log)