From: Piotr Caban <piotr@codeweavers.com>
Subject: [PATCH] msvcrt: Improve acosf compatibility with native ucrtbase.
Message-Id: <d2859d14-1266-741c-c8e0-f93d49777dfb@codeweavers.com>
Date: Thu, 25 Feb 2021 15:39:23 +0100


It reduces number of different acosf results from 5678739 to 240905.

Signed-off-by: Piotr Caban <piotr@codeweavers.com>
---
  dlls/msvcrt/math.c | 57 +++++++++++++++++-----------------------------
  1 file changed, 21 insertions(+), 36 deletions(-)

diff --git a/dlls/msvcrt/math.c b/dlls/msvcrt/math.c
index b1bf60d57ea..0543b2ce87c 100644
--- a/dlls/msvcrt/math.c
+++ b/dlls/msvcrt/math.c
@@ -287,28 +287,29 @@ int CDECL _isnanf( float num )
     return (u.i & 0x7fffffff) > 0x7f800000;
 }
 
-/*********************************************************************
- *      acosf (MSVCRT.@)
- *
- * Copied from musl: src/math/acosf.c
- */
-static float acosf_R(float z)
+static float asinf_R(float z)
 {
-    static const float pS0 = 1.6666586697e-01,
-                 pS1 = -4.2743422091e-02,
-                 pS2 = -8.6563630030e-03,
-                 qS1 = -7.0662963390e-01;
+    /* coefficients for R(x^2) */
+    static const float p1 = 1.66666672e-01,
+                 p2 = -5.11644611e-02,
+                 p3 = -1.21124933e-02,
+                 p4 = -3.58742251e-03,
+                 q1 = -7.56982703e-01;
 
     float p, q;
-    p = z * (pS0 + z * (pS1 + z * pS2));
-    q = 1.0f + z * qS1;
+    p = z * (p1 + z * (p2 + z * (p3 + z * p4)));
+    q = 1.0f + z * q1;
     return p / q;
 }
 
+/*********************************************************************
+ *      acosf (MSVCRT.@)
+ *
+ * Copied from musl: src/math/acosf.c
+ */
 float CDECL acosf( float x )
 {
-    static const float pio2_hi = 1.5707962513e+00,
-                 pio2_lo = 7.5497894159e-08;
+    static const double pio2_lo = 6.12323399573676603587e-17;
 
     float z, w, s, c, df;
     unsigned int hx, ix;
@@ -319,7 +320,7 @@ float CDECL acosf( float x )
     if (ix >= 0x3f800000) {
         if (ix == 0x3f800000) {
             if (hx >> 31)
-                return 2 * pio2_lo + 2 * pio2_hi + 7.5231638453e-37;
+                return M_PI;
             return 0;
         }
         if (isnan(x)) return x;
@@ -328,23 +329,22 @@ float CDECL acosf( float x )
     /* |x| < 0.5 */
     if (ix < 0x3f000000) {
         if (ix <= 0x32800000) /* |x| < 2**-26 */
-            return pio2_lo + pio2_hi + 7.5231638453e-37;
-        return pio2_hi - (x - (pio2_lo - x * acosf_R(x * x)));
+            return M_PI_2;
+        return M_PI_2 - (x - (pio2_lo - x * asinf_R(x * x)));
     }
     /* x < -0.5 */
     if (hx >> 31) {
         z = (1 + x) * 0.5f;
         s = sqrtf(z);
-        w = acosf_R(z) * s - pio2_lo;
-        return 2 * (pio2_hi - (s + w));
+        return M_PI - 2 * (s + ((double)s * asinf_R(z)));
     }
     /* x > 0.5 */
     z = (1 - x) * 0.5f;
     s = sqrtf(z);
-    hx = *(unsigned int*)&s & 0xfffff000;
+    hx = *(unsigned int*)&s & 0xffff0000;
     df = *(float*)&hx;
     c = (z - df * df) / (s + df);
-    w = acosf_R(z) * s + c;
+    w = asinf_R(z) * s + c;
     return 2 * (df + w);
 }
 
@@ -353,21 +353,6 @@ float CDECL acosf( float x )
  *
  * Copied from musl: src/math/asinf.c
  */
-static float asinf_R(float z)
-{
-    /* coefficients for R(x^2) */
-    static const float p1 = 1.66666672e-01,
-                 p2 = -5.11644611e-02,
-                 p3 = -1.21124933e-02,
-                 p4 = -3.58742251e-03,
-                 q1 = -7.56982703e-01;
-
-    float p, q;
-    p = z * (p1 + z * (p2 + z * (p3 + z * p4)));
-    q = 1.0f + z * q1;
-    return p / q;
-}
-
 float CDECL asinf( float x )
 {
     static const double pio2 = 1.570796326794896558e+00;