1 /* e_sqrtf.c -- float version of e_sqrt.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 3 */ 4 5 /* 6 * ==================================================== 7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 8 * 9 * Developed at SunPro, a Sun Microsystems, Inc. business. 10 * Permission to use, copy, modify, and distribute this 11 * software is freely granted, provided that this notice 12 * is preserved. 13 * ==================================================== 14 */ 15 16 #include <sys/cdefs.h> 17 #if defined(LIBM_SCCS) && !defined(lint) 18 __RCSID("$NetBSD: e_sqrtf.c,v 1.7 2002/05/26 22:01:53 wiz Exp $"); 19 #endif 20 21 #include "math.h" 22 #include "math_private.h" 23 24 static const float one = 1.0, tiny=1.0e-30; 25 26 float 27 __ieee754_sqrtf(float x) 28 { 29 float z; 30 int32_t sign = (int)0x80000000; 31 int32_t ix,s,q,m,t,i; 32 u_int32_t r; 33 34 GET_FLOAT_WORD(ix,x); 35 36 /* take care of Inf and NaN */ 37 if((ix&0x7f800000)==0x7f800000) { 38 return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf 39 sqrt(-inf)=sNaN */ 40 } 41 /* take care of zero */ 42 if(ix<=0) { 43 if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */ 44 else if(ix<0) 45 return (x-x)/(x-x); /* sqrt(-ve) = sNaN */ 46 } 47 /* normalize x */ 48 m = (ix>>23); 49 if(m==0) { /* subnormal x */ 50 for(i=0;(ix&0x00800000)==0;i++) ix<<=1; 51 m -= i-1; 52 } 53 m -= 127; /* unbias exponent */ 54 ix = (ix&0x007fffff)|0x00800000; 55 if(m&1) /* odd m, double x to make it even */ 56 ix += ix; 57 m >>= 1; /* m = [m/2] */ 58 59 /* generate sqrt(x) bit by bit */ 60 ix += ix; 61 q = s = 0; /* q = sqrt(x) */ 62 r = 0x01000000; /* r = moving bit from right to left */ 63 64 while(r!=0) { 65 t = s+r; 66 if(t<=ix) { 67 s = t+r; 68 ix -= t; 69 q += r; 70 } 71 ix += ix; 72 r>>=1; 73 } 74 75 /* use floating add to find out rounding direction */ 76 if(ix!=0) { 77 z = one-tiny; /* trigger inexact flag */ 78 if (z>=one) { 79 z = one+tiny; 80 if (z>one) 81 q += 2; 82 else 83 q += (q&1); 84 } 85 } 86 ix = (q>>1)+0x3f000000; 87 ix += (m <<23); 88 SET_FLOAT_WORD(z,ix); 89 return z; 90 } 91