msvcrt: Import atanf from musl.

Signed-off-by: Piotr Caban <piotr@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/msvcrt/math.c

@@ -330,12 +330,91 @@ float CDECL MSVCRT_asinf( float x )
 
 /*********************************************************************
  *      MSVCRT_atanf (MSVCRT.@)
+ *
+ * Copied from musl: src/math/atanf.c
  */
+static inline float fp_barrierf(float x)
+{
+    volatile float y = x;
+    return y;
+}
 float CDECL MSVCRT_atanf( float x )
 {
-  float ret = atanf(x);
-  if (!finitef(x)) return math_error(_DOMAIN, "atanf", x, 0, ret);
-  return ret;
+    static const float atanhi[] = {
+        4.6364760399e-01,
+        7.8539812565e-01,
+        9.8279368877e-01,
+        1.5707962513e+00,
+    };
+    static const float atanlo[] = {
+        5.0121582440e-09,
+        3.7748947079e-08,
+        3.4473217170e-08,
+        7.5497894159e-08,
+    };
+    static const float aT[] = {
+        3.3333328366e-01,
+        -1.9999158382e-01,
+        1.4253635705e-01,
+        -1.0648017377e-01,
+        6.1687607318e-02,
+    };
+
+    float w, s1, s2, z;
+    unsigned int ix, sign;
+    int id;
+
+#if _MSVCR_VER == 0
+    if (MSVCRT__isnanf(x)) return math_error(_DOMAIN, "atanf", x, 0, x);
+#endif
+
+    ix = *(unsigned int*)&x;
+    sign = ix >> 31;
+    ix &= 0x7fffffff;
+    if (ix >= 0x4c800000) {  /* if |x| >= 2**26 */
+        if (MSVCRT__isnanf(x))
+            return x;
+        z = atanhi[3] + 7.5231638453e-37;
+        return sign ? -z : z;
+    }
+    if (ix < 0x3ee00000) {   /* |x| < 0.4375 */
+        if (ix < 0x39800000) {  /* |x| < 2**-12 */
+            if (ix < 0x00800000)
+                /* raise underflow for subnormal x */
+                fp_barrierf(x*x);
+            return x;
+        }
+        id = -1;
+    } else {
+        x = fabsf(x);
+        if (ix < 0x3f980000) {  /* |x| < 1.1875 */
+            if (ix < 0x3f300000) {  /*  7/16 <= |x| < 11/16 */
+                id = 0;
+                x = (2.0f * x - 1.0f) / (2.0f + x);
+            } else {                /* 11/16 <= |x| < 19/16 */
+                id = 1;
+                x = (x - 1.0f) / (x + 1.0f);
+            }
+        } else {
+            if (ix < 0x401c0000) {  /* |x| < 2.4375 */
+                id = 2;
+                x = (x - 1.5f) / (1.0f + 1.5f * x);
+            } else {                /* 2.4375 <= |x| < 2**26 */
+                id = 3;
+                x = -1.0f / x;
+            }
+        }
+    }
+    /* end of argument reduction */
+    z = x * x;
+    w = z * z;
+    /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
+    s1 = z * (aT[0] + w * (aT[2] + w * aT[4]));
+    s2 = w * (aT[1] + w * aT[3]);
+    if (id < 0)
+        return x - x * (s1 + s2);
+    z = atanhi[id] - ((x * (s1 + s2) - atanlo[id]) - x);
+    return sign ? -z : z;
 }
 
 /*********************************************************************