| The Android Open Source Project | 1dc9e47 | 2009-03-03 19:28:35 -0800 | [diff] [blame^] | 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 | #ifndef lint |
| 17 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_sqrtf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $"; |
| 18 | #endif |
| 19 | |
| 20 | #include "math.h" |
| 21 | #include "math_private.h" |
| 22 | |
| 23 | static const float one = 1.0, tiny=1.0e-30; |
| 24 | |
| 25 | float |
| 26 | __ieee754_sqrtf(float x) |
| 27 | { |
| 28 | float z; |
| 29 | int32_t sign = (int)0x80000000; |
| 30 | int32_t ix,s,q,m,t,i; |
| 31 | u_int32_t r; |
| 32 | |
| 33 | GET_FLOAT_WORD(ix,x); |
| 34 | |
| 35 | /* take care of Inf and NaN */ |
| 36 | if((ix&0x7f800000)==0x7f800000) { |
| 37 | return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf |
| 38 | sqrt(-inf)=sNaN */ |
| 39 | } |
| 40 | /* take care of zero */ |
| 41 | if(ix<=0) { |
| 42 | if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */ |
| 43 | else if(ix<0) |
| 44 | return (x-x)/(x-x); /* sqrt(-ve) = sNaN */ |
| 45 | } |
| 46 | /* normalize x */ |
| 47 | m = (ix>>23); |
| 48 | if(m==0) { /* subnormal x */ |
| 49 | for(i=0;(ix&0x00800000)==0;i++) ix<<=1; |
| 50 | m -= i-1; |
| 51 | } |
| 52 | m -= 127; /* unbias exponent */ |
| 53 | ix = (ix&0x007fffff)|0x00800000; |
| 54 | if(m&1) /* odd m, double x to make it even */ |
| 55 | ix += ix; |
| 56 | m >>= 1; /* m = [m/2] */ |
| 57 | |
| 58 | /* generate sqrt(x) bit by bit */ |
| 59 | ix += ix; |
| 60 | q = s = 0; /* q = sqrt(x) */ |
| 61 | r = 0x01000000; /* r = moving bit from right to left */ |
| 62 | |
| 63 | while(r!=0) { |
| 64 | t = s+r; |
| 65 | if(t<=ix) { |
| 66 | s = t+r; |
| 67 | ix -= t; |
| 68 | q += r; |
| 69 | } |
| 70 | ix += ix; |
| 71 | r>>=1; |
| 72 | } |
| 73 | |
| 74 | /* use floating add to find out rounding direction */ |
| 75 | if(ix!=0) { |
| 76 | z = one-tiny; /* trigger inexact flag */ |
| 77 | if (z>=one) { |
| 78 | z = one+tiny; |
| 79 | if (z>one) |
| 80 | q += 2; |
| 81 | else |
| 82 | q += (q&1); |
| 83 | } |
| 84 | } |
| 85 | ix = (q>>1)+0x3f000000; |
| 86 | ix += (m <<23); |
| 87 | SET_FLOAT_WORD(z,ix); |
| 88 | return z; |
| 89 | } |