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-rw-r--r--src/math/sqrtf.c84
1 files changed, 84 insertions, 0 deletions
diff --git a/src/math/sqrtf.c b/src/math/sqrtf.c
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+/* origin: FreeBSD /usr/src/lib/msun/src/e_sqrtf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#include "libm.h"
+
+static const float one = 1.0, tiny = 1.0e-30;
+
+float sqrtf(float x)
+{
+ float z;
+ int32_t sign = (int)0x80000000;
+ int32_t ix,s,q,m,t,i;
+ uint32_t r;
+
+ GET_FLOAT_WORD(ix, x);
+
+ /* take care of Inf and NaN */
+ if ((ix&0x7f800000) == 0x7f800000)
+ return x*x + x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf, sqrt(-inf)=sNaN */
+
+ /* take care of zero */
+ if (ix <= 0) {
+ if ((ix&~sign) == 0)
+ return x; /* sqrt(+-0) = +-0 */
+ if (ix < 0)
+ return (x-x)/(x-x); /* sqrt(-ve) = sNaN */
+ }
+ /* normalize x */
+ m = ix>>23;
+ if (m == 0) { /* subnormal x */
+ for (i = 0; (ix&0x00800000) == 0; i++)
+ ix<<=1;
+ m -= i - 1;
+ }
+ m -= 127; /* unbias exponent */
+ ix = (ix&0x007fffff)|0x00800000;
+ if (m&1) /* odd m, double x to make it even */
+ ix += ix;
+ m >>= 1; /* m = [m/2] */
+
+ /* generate sqrt(x) bit by bit */
+ ix += ix;
+ q = s = 0; /* q = sqrt(x) */
+ r = 0x01000000; /* r = moving bit from right to left */
+
+ while (r != 0) {
+ t = s + r;
+ if (t <= ix) {
+ s = t+r;
+ ix -= t;
+ q += r;
+ }
+ ix += ix;
+ r >>= 1;
+ }
+
+ /* use floating add to find out rounding direction */
+ if (ix != 0) {
+ z = one - tiny; /* raise inexact flag */
+ if (z >= one) {
+ z = one + tiny;
+ if (z > one)
+ q += 2;
+ else
+ q += q & 1;
+ }
+ }
+ ix = (q>>1) + 0x3f000000;
+ ix += m << 23;
+ SET_FLOAT_WORD(z, ix);
+ return z;
+}