msvcrt: Import atan2f from musl.

dlls/msvcrt/math.c

@@ -340,12 +340,73 @@ float CDECL MSVCRT_atanf( float x )
 
 /*********************************************************************
  *              MSVCRT_atan2f (MSVCRT.@)
+ *
+ * Copied from musl: src/math/atan2f.c
  */
-float CDECL MSVCRT_atan2f( float x, float y )
+float CDECL MSVCRT_atan2f( float y, float x )
 {
-  float ret = atan2f(x, y);
-  if (isnan(x)) return math_error(_DOMAIN, "atan2f", x, y, ret);
-  return ret;
+    static const float pi     = 3.1415927410e+00,
+                 pi_lo  = -8.7422776573e-08;
+
+    float z;
+    unsigned int m, ix, iy;
+
+    if (MSVCRT__isnanf(x) || MSVCRT__isnanf(y))
+        return x + y;
+    ix = *(unsigned int*)&x;
+    iy = *(unsigned int*)&y;
+    if (ix == 0x3f800000)  /* x=1.0 */
+        return atanf(y);
+    m = ((iy >> 31) & 1) | ((ix >> 30) & 2);  /* 2*sign(x)+sign(y) */
+    ix &= 0x7fffffff;
+    iy &= 0x7fffffff;
+
+    /* when y = 0 */
+    if (iy == 0) {
+        switch (m) {
+        case 0:
+        case 1: return y;   /* atan(+-0,+anything)=+-0 */
+        case 2: return pi;  /* atan(+0,-anything) = pi */
+        case 3: return -pi; /* atan(-0,-anything) =-pi */
+        }
+    }
+    /* when x = 0 */
+    if (ix == 0)
+        return m & 1 ? -pi / 2 : pi / 2;
+    /* when x is INF */
+    if (ix == 0x7f800000) {
+        if (iy == 0x7f800000) {
+            switch (m) {
+            case 0: return pi / 4;      /* atan(+INF,+INF) */
+            case 1: return -pi / 4;     /* atan(-INF,+INF) */
+            case 2: return 3 * pi / 4;  /*atan(+INF,-INF)*/
+            case 3: return -3 * pi / 4; /*atan(-INF,-INF)*/
+            }
+        } else {
+            switch (m) {
+            case 0: return 0.0f;    /* atan(+...,+INF) */
+            case 1: return -0.0f;   /* atan(-...,+INF) */
+            case 2: return pi;      /* atan(+...,-INF) */
+            case 3: return -pi;     /* atan(-...,-INF) */
+            }
+        }
+    }
+    /* |y/x| > 0x1p26 */
+    if (ix + (26 << 23) < iy || iy == 0x7f800000)
+        return m & 1 ? -pi / 2 : pi / 2;
+
+    /* z = atan(|y/x|) with correct underflow */
+    if ((m & 2) && iy + (26 << 23) < ix)  /*|y/x| < 0x1p-26, x < 0 */
+        z = 0.0;
+    else
+        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(-,-) */
+    }
 }
 
 /*********************************************************************