first commit of the new libm!

[musl] / src / math / atan2f.c

diff --git a/src/math/atan2f.c b/src/math/atan2f.c
new file mode 100644 (file)
index 0000000..4d78840
--- /dev/null
+++ b/src/math/atan2f.c
@@ -0,0 +1,93 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.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 volatile float
+tiny = 1.0e-30;
+static const float
+zero = 0.0,
+pi_o_4 = 7.8539818525e-01, /* 0x3f490fdb */
+pi_o_2 = 1.5707963705e+00, /* 0x3fc90fdb */
+pi     = 3.1415927410e+00; /* 0x40490fdb */
+static volatile float
+pi_lo  = -8.7422776573e-08; /* 0xb3bbbd2e */
+
+float atan2f(float y, float x)
+{
+       float z;
+       int32_t k,m,hx,hy,ix,iy;
+
+       GET_FLOAT_WORD(hx, x);
+       ix = hx & 0x7fffffff;
+       GET_FLOAT_WORD(hy, y);
+       iy = hy & 0x7fffffff;
+       if (ix > 0x7f800000 || iy > 0x7f800000)  /* x or y is NaN */
+               return x+y;
+       if (hx == 0x3f800000)  /* x=1.0 */
+               return atanf(y);
+       m = ((hy>>31)&1) | ((hx>>30)&2);  /* 2*sign(x)+sign(y) */
+
+       /* when y = 0 */
+       if (iy == 0) {
+               switch (m) {
+               case 0:
+               case 1: return y;        /* atan(+-0,+anything)=+-0 */
+               case 2: return  pi+tiny; /* atan(+0,-anything) = pi */
+               case 3: return -pi-tiny; /* atan(-0,-anything) =-pi */
+               }
+       }
+       /* when x = 0 */
+       if (ix == 0)
+               return hy < 0 ? -pi_o_2-tiny : pi_o_2+tiny;
+       /* when x is INF */
+       if (ix == 0x7f800000) {
+               if (iy == 0x7f800000) {
+                       switch (m) {
+                       case 0: return  pi_o_4+tiny; /* atan(+INF,+INF) */
+                       case 1: return -pi_o_4-tiny; /* atan(-INF,+INF) */
+                       case 2: return (float)3.0*pi_o_4+tiny;  /*atan(+INF,-INF)*/
+                       case 3: return (float)-3.0*pi_o_4-tiny; /*atan(-INF,-INF)*/
+                       }
+               } else {
+                       switch (m) {
+                       case 0: return  zero;    /* atan(+...,+INF) */
+                       case 1: return -zero;    /* atan(-...,+INF) */
+                       case 2: return  pi+tiny; /* atan(+...,-INF) */
+                       case 3: return -pi-tiny; /* atan(-...,-INF) */
+                       }
+               }
+       }
+       /* when y is INF */
+       if (iy == 0x7f800000)
+               return hy < 0 ? -pi_o_2-tiny : pi_o_2+tiny;
+
+       /* compute y/x */
+       k = (iy-ix)>>23;
+       if (k > 26) {                  /* |y/x| >  2**26 */
+               z = pi_o_2+(float)0.5*pi_lo;
+               m &= 1;
+       } else if (k < -26 && hx < 0)  /* 0 > |y|/x > -2**-26 */
+               z = 0.0;
+       else                           /* safe to do y/x */
+               z = atanf(fabsf(y/x));
+       switch (m) {
+       case 0: return z;              /* atan(+,+) */
+       case 1: return -z;             /* atan(-,+) */
+       case 2: return pi - (z-pi_lo); /* atan(+,-) */
+       default: /* case 3 */
+               return (z-pi_lo) - pi; /* atan(-,-) */
+       }
+}