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 "math.h" 17 #include "math_private.h" 18 19 static const float one = 1.0, tiny=1.0e-30; 20 21 float 22 sqrtf(float x) 23 { 24 float z; 25 int32_t sign = (int)0x80000000; 26 int32_t ix,s,q,m,t,i; 27 u_int32_t r; 28 29 GET_FLOAT_WORD(ix,x); 30 31 /* take care of Inf and NaN */ 32 if((ix&0x7f800000)==0x7f800000) { 33 return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf 34 sqrt(-inf)=sNaN */ 35 } 36 /* take care of zero */ 37 if(ix<=0) { 38 if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */ 39 else if(ix<0) 40 return (x-x)/(x-x); /* sqrt(-ve) = sNaN */ 41 } 42 /* normalize x */ 43 m = (ix>>23); 44 if(m==0) { /* subnormal x */ 45 for(i=0;(ix&0x00800000)==0;i++) ix<<=1; 46 m -= i-1; 47 } 48 m -= 127; /* unbias exponent */ 49 ix = (ix&0x007fffff)|0x00800000; 50 if(m&1) /* odd m, double x to make it even */ 51 ix += ix; 52 m >>= 1; /* m = [m/2] */ 53 54 /* generate sqrt(x) bit by bit */ 55 ix += ix; 56 q = s = 0; /* q = sqrt(x) */ 57 r = 0x01000000; /* r = moving bit from right to left */ 58 59 while(r!=0) { 60 t = s+r; 61 if(t<=ix) { 62 s = t+r; 63 ix -= t; 64 q += r; 65 } 66 ix += ix; 67 r>>=1; 68 } 69 70 /* use floating add to find out rounding direction */ 71 if(ix!=0) { 72 z = one-tiny; /* trigger inexact flag */ 73 if (z>=one) { 74 z = one+tiny; 75 if (z>one) 76 q += 2; 77 else 78 q += (q&1); 79 } 80 } 81 ix = (q>>1)+0x3f000000; 82 ix += (m <<23); 83 SET_FLOAT_WORD(z,ix); 84 return z; 85 } 86