kernel/math/sqrt.c

/* */
This source file includes following definitions.
shift_right
sqr64
fsqrt
   1 /*
   2  * linux/kernel/math/sqrt.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6 
   7 /*
   8  * simple and stupid temporary real fsqrt() routine
   9  *
  10  * There are probably better ways to do this, but this should work ok.
  11  */
  12 
  13 #include <linux/math_emu.h>
  14 #include <linux/sched.h>
  15 
  16 static void shift_right(int * c)
     /*  */
  17 {
  18         __asm__("shrl $1,12(%0) ; rcrl $1,8(%0) ; rcrl $1,4(%0) ; rcrl $1,(%0)"
  19                 ::"r" ((long) c));
  20 }
  21 
  22 static int sqr64(unsigned long * a, unsigned long * b)
     /*  */
  23 {
  24         unsigned long tmp[4];
  25 
  26         __asm__("movl (%0),%%eax  ; mull %%eax\n\t"
  27                 "movl %%eax,(%1)   ; movl %%edx,4(%1)\n\t"
  28                 "movl 4(%0),%%eax ; mull %%eax\n\t"
  29                 "movl %%eax,8(%1)  ; movl %%edx,12(%1)\n\t"
  30                 "movl (%0),%%eax  ; mull 4(%0)\n\t"
  31                 "addl %%eax,%%eax   ; adcl %%edx,%%edx\n\t"
  32                 "adcl $0,12(%1)   ; addl %%eax,4(%1)\n\t"
  33                 "adcl %%edx,8(%1)  ; adcl $0,12(%1)"
  34                 ::"b" ((long) a),"c" ((long) tmp)
  35                 :"ax","bx","cx","dx");
  36         if (tmp[3] > b[3] ||
  37            (tmp[3] == b[3] && (tmp[2] > b[2] ||
  38            (tmp[2] == b[2] && (tmp[1] > b[1] ||
  39            (tmp[1] == b[1] && tmp[0] > b[0]))))))
  40                 return 0;
  41         return 1;
  42 }
  43 
  44 void fsqrt(const temp_real * s, temp_real * d)
     /*  */
  45 {
  46         unsigned long src[4];
  47         unsigned long res[2];
  48         int exponent;
  49         unsigned long mask, *c;
  50         int i;
  51 
  52         exponent = s->exponent;
  53         src[0] = src[1] = 0;
  54         src[2] = s->a;
  55         src[3] = s->b;
  56         d->exponent = 0;
  57         d->a = d->b = 0;
  58         if (!exponent)          /* fsqrt(0.0) = 0.0 */
  59                 return;
  60         if (!src[2] && !src[3])
  61                 return;
  62         if (exponent & 0x8000) {
  63                 send_sig(SIGFPE,current,0);
  64                 return;
  65         }
  66         if (exponent & 1) {
  67                 shift_right(src);
  68                 exponent++;
  69         }
  70         exponent >>= 1;
  71         exponent += 0x1fff;
  72         c = res + 2;
  73         mask = 0;
  74         for (i = 64 ; i > 0 ; i--) {
  75                 if (!(mask >>= 1)) {
  76                         c--;
  77                         mask = 0x80000000;
  78                 }
  79                 res[0] = d->a; res[1] = d->b;
  80                 *c |= mask;
  81                 if (sqr64(res,src)) {
  82                         d->a = res[0];
  83                         d->b = res[1];
  84                 }
  85         }
  86         if (!d->a && !d->b)
  87                 return;
  88         while (!(d->b & 0x80000000)) {
  89                 __asm__("addl %%eax,%%eax ; adcl %%edx,%%edx"
  90                         :"=a" (d->a),"=d" (d->b)
  91                         :"0" (d->a),"1" (d->b));
  92                 exponent--;
  93         }
  94         d->exponent = exponent;
  95 }
/* */
root/kernel/math/sqrt.c

DEFINITIONS
