first commit of the new libm!

[musl] / src / math / sqrtf.c

diff --git a/src/math/sqrtf.c b/src/math/sqrtf.c
new file mode 100644 (file)
index 0000000..35c24e5
--- /dev/null
+++ b/src/math/sqrtf.c
@@ -0,0 +1,84 @@
+/* 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;
+}