From 1073b379c888a912867e31bc9c40a7f78cac231e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tyge=20L=C3=B8vset?= <tylo@norceresearch.no>
Date: Sat, 14 Nov 2020 00:02:58 +0100
Subject: [PATCH] WIN32/64 only: Added C99 math functions: tgamma(), tgammaf(),
 lgamma(), lgammaf(), cbrt(), cbrtf(), log2(), log2f(), exp2(), exp2f(). The
 gamma() functions are accurate to 13 digits over the full range. Returns
 INFINITY / NAN identical to other compiler's math libs.

#include <stdio.h>
#include <math.h>

int main() {
  double x;
  for (x = -7.0; x <= 520.0; x += 1.0) {
    printf("tgamma/lgamma %6.3f: %20.13g  %20.13g\n", x/3, tgamma(x/3.0), lgamma(x/3.0));
  }
  printf("tgamma/lgamma %g: %20.13g  %20.13g\n", 0.00000234, tgamma(0.00000234), lgamma(0.00000234));
  printf("log2, exp2, cbrt, cbrt: %.15g %.15g %.15g %.15g\n", log2(1024), exp2(10), cbrt(-10), cbrt(10));
}
---
 .gitignore                   |  3 ++
 win32/include/tcc/tcc_libm.h | 65 ++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)

diff --git a/.gitignore b/.gitignore
index c4732645..52e6d558 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,13 +31,16 @@ tcc-doc.html
 tcc-doc.info
 
 win32/doc
+win32/examples/libtcc_test.c
 win32/libtcc
 win32/lib/32
 win32/lib/64
 win32/include/float.h
+win32/include/stdalign.h
 win32/include/stdarg.h
 win32/include/stdbool.h
 win32/include/stddef.h
+win32/include/stdnoreturn.h
 win32/include/varargs.h
 win32/include/tcclib.h
 
diff --git a/win32/include/tcc/tcc_libm.h b/win32/include/tcc/tcc_libm.h
index 0a62e6fb..90e26c47 100644
--- a/win32/include/tcc/tcc_libm.h
+++ b/win32/include/tcc/tcc_libm.h
@@ -198,4 +198,69 @@ __CRT_INLINE long long __cdecl llroundl (long double x) {
   End of code based on MUSL
 *******************************************************************************/
 
+
+__CRT_INLINE double __cdecl cbrt(double x) {
+  return (1.0 - ((x < 0.0) << 1)) * pow(fabs(x), 1.0 / 3.0);
+}
+__CRT_INLINE float __cdecl cbrtf(float x) {
+  return (1.0f - ((x < 0.0f) << 1)) * (float) pow(fabs(x), 1.0 / 3.0);
+}
+
+__CRT_INLINE double __cdecl log2(double x) {
+  return log(x) * 1.4426950408889634073599246810019;
+}
+__CRT_INLINE float __cdecl log2f(float x) {
+  return logf(x) * 1.4426950408889634073599246810019f;
+}
+
+__CRT_INLINE double __cdecl exp2(double x) {
+  return exp(x * 0.69314718055994530941723212145818);
+}
+__CRT_INLINE float __cdecl exp2f(float x) {
+  return expf(x * 0.69314718055994530941723212145818f);
+}
+
+/* tgamma and lgamma: Lanczos approximation
+ * https://rosettacode.org/wiki/Gamma_function
+ * https://www.johndcook.com/blog/cpp_gamma
+ */
+__CRT_INLINE double __cdecl lgamma(double x);
+
+__CRT_INLINE double __cdecl tgamma(double x) {
+  double m = 1.0, t = 3.14159265358979323;
+  if (x == (int)x) {
+    for (int k = 2; k < x; ++k) m *= k;
+    return x > 0.0 ? m : (x == 0.0 ? INFINITY : NAN);
+  }
+  if (x < 0.5)
+    return t / (sin(t * x) * tgamma(1.0 - x));
+  if (x > 12.0)
+    return exp(lgamma(x));
+  static const double c[8] = {676.5203681218851, -1259.1392167224028,
+                              771.32342877765313, -176.61502916214059,
+                              12.507343278686905, -0.13857109526572012,
+                              9.9843695780195716e-6, 1.5056327351493116e-7};
+  m = 0.99999999999980993, t = x + (8 - 1.5);
+  for (int k = 0; k < 8; ++k) m += c[k] / (x + k);
+  return 2.50662827463100050 * pow(t, x - 0.5) * exp(-t) * m; /* sqrt(2pi) */
+}
+
+__CRT_INLINE double __cdecl lgamma(double x) {
+  if (x < 12.0)
+    return x <= 0.0 && x == (int)x ? INFINITY : log(fabs(tgamma(x)));
+  static const double c[7] = {1.0/12.0, -1.0/360.0, 1.0/1260.0, -1.0/1680.0,
+                              1.0/1188.0, -691.0/360360.0, 1.0/156.0};
+  double m = -3617.0/122400.0, z = 1.0 / (x * x);
+  for (int k = 6; k >= 0; --k) m = m * z + c[k];
+  return (x - 0.5) * log(x) - x + 0.918938533204672742 + m / x; /* log(2pi)/2 */
+}
+
+__CRT_INLINE float __cdecl tgammaf(float x) {
+  return tgamma(x);
+}
+
+__CRT_INLINE float __cdecl lgammaf(float x) {
+  return lgamma(x);
+}
+
 #endif /* _TCC_LIBM_H_ */