[libc] Implement some math.h functions with builtins

This commit adds implementation of some of the basic math.h functions
with compiler builtins.

configs/user-debug.yaml

@@ -6,7 +6,6 @@ variables:
 
   ccflags: [
     "--target=x86_64-jsix-elf",
-    "-mno-sse",
     "-fno-omit-frame-pointer",
     "-fno-stack-protector",
 

src/libraries/libc/math.h

@@ -12,8 +12,12 @@
 
 // NOTE: libc math.h is only stubbed out currently!
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #define NAN 0
-#define INFINITY 0
+#define INFINITY        __builtin_inff()
 
 #define FP_NAN     (-1)
 #define FP_ZERO      0
@@ -25,7 +29,7 @@
 typedef float float_t;
 typedef double double_t;
 
-#define isinf(x)       0
+#define isinf(x)       (__builtin_isinf_sign((x)) != 0)
 #define isnan(x)       0
 #define isnormal(x)    0
 
@@ -38,7 +42,7 @@ typedef double double_t;
                         FP_SUBNORMAL)
 
 
-#define signbit(x)     0
+#define signbit(x)     (__builtin_signbit((x)))
 
 
 double acos(double x);
@@ -265,3 +269,8 @@ long double fminl(long double x, long double y);
 double fma(double x, double y, double z);
 float fmaf(float x, float y, float z);
 long double fmal(long double x, long double y, long double z);
+
+
+#ifdef __cplusplus
+} // extern C
+#endif

src/libraries/libc/math/builtins.cpp.cog

@@ -0,0 +1,42 @@
+// vim: ft=cpp
+#include <math.h>
+
+/*[[[cog code generation
+
+builtins_single = [
+    "acos", "asin", "atan", "ceil", "cos", "cosh", "exp", "fabs",
+    "floor", "log10", "log", "sin", "sinh", "sqrt", "tan", "tanh",
+    ]
+
+builtins_double = ["atan2", "fmod", "pow"]
+
+builtins_intp = [
+    "frexp", "ldexp", "modf", 
+    ]
+
+for fname in builtins_single:
+    cog.outl(f"double      {fname}  (double x)      {{ return __builtin_{fname}(x); }}")
+    cog.outl(f"float       {fname}f (float x)       {{ return __builtin_{fname}f(x); }}")
+    cog.outl(f"long double {fname}l (long double x) {{ return __builtin_{fname}l(x); }}")
+    cog.outl()
+
+for fname in builtins_double:
+    cog.outl(f"double      {fname}  (double x, double y)           {{ return __builtin_{fname}(x, y); }}")
+    cog.outl(f"float       {fname}f (float x, float y)             {{ return __builtin_{fname}f(x, y); }}")
+    cog.outl(f"long double {fname}l (long double x, long double y) {{ return __builtin_{fname}l(x, y); }}")
+    cog.outl()
+
+]]]*/
+/// [[[end]]]
+
+double frexp(double value, int *exp)                    { return __builtin_frexp(value, exp); }
+float frexpf(float value, int *exp)                     { return __builtin_frexpf(value, exp); }
+long double frexpl(long double value, int *exp)         { return __builtin_frexpl(value, exp); }
+
+double ldexp(double x, int exp)                         { return __builtin_ldexp(x, exp); }
+float ldexpf(float x, int exp)                          { return __builtin_ldexpf(x, exp); }
+long double ldexpl(long double x, int exp)              { return __builtin_ldexpl(x, exp); }
+
+double modf(double value, double *iptr)                 { return __builtin_modf(value, iptr); }
+float modff(float value, float *iptr)                   { return __builtin_modff(value, iptr); }
+long double modfl(long double value, long double *iptr) { return __builtin_modfl(value, iptr); }