From e4146267fa1a71fe0aaadbc8aadcfdd58eb9deed Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Sat, 16 Nov 2013 18:56:02 -0800
Subject: [PATCH] Fixed bug 2245 - add SDL_acos and SDL_asin

Sylvain

Here's some code to add arc cosine, and arc sin functions to SDL_stdlib.c
There are plainly written using SDL_atan.
---
 include/SDL_stdinc.h |  2 ++
 src/libm/s_atan.c    | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/SDL_stdinc.h b/include/SDL_stdinc.h
index f0780a217..9a421ba63 100644
--- a/include/SDL_stdinc.h
+++ b/include/SDL_stdinc.h
@@ -340,6 +340,8 @@ extern DECLSPEC int SDLCALL SDL_vsnprintf(char *text, size_t maxlen, const char
 #endif
 #endif
 
+extern DECLSPEC double SDLCALL SDL_acos(double x);
+extern DECLSPEC double SDLCALL SDL_asin(double x);
 extern DECLSPEC double SDLCALL SDL_atan(double x);
 extern DECLSPEC double SDLCALL SDL_atan2(double x, double y);
 extern DECLSPEC double SDLCALL SDL_ceil(double x);
diff --git a/src/libm/s_atan.c b/src/libm/s_atan.c
index f664f0eb3..2f24b29b0 100644
--- a/src/libm/s_atan.c
+++ b/src/libm/s_atan.c
@@ -112,3 +112,29 @@ double atan(double x)
 	}
 }
 libm_hidden_def(atan)
+
+double SDL_acos(double val)
+{
+    double result;
+    if (val == -1.0) {
+        result = M_PI;
+    } else {
+        result = SDL_atan(SDL_sqrt(1.0 - val * val) / val);
+        if (result < 0.0)
+        {
+            result += M_PI;
+        }
+    }
+    return result;
+}
+
+double SDL_asin(double val)
+{
+    double result;
+    if (val == -1.0) {
+        result = -(M_PI / 2.0);
+    } else {
+        result = (M_PI / 2.0) - SDL_acos(val);
+    }
+    return result;
+}