py/modmath: Work around msvc float bugs in atan2, fmod and modf.

Older implementations deal with infinity/negative zero incorrectly.  This
commit adds generic fixes that can be enabled by any port that needs them,
along with new tests cases.

ports/windows/mpconfigport.h

@@ -227,6 +227,14 @@ extern const struct _mp_obj_module_t mp_module_time;
 #define MP_SSIZE_MAX                _I32_MAX
 #endif
 
+// VC++ 12.0 fixes
+#if (_MSC_VER <= 1800)
+#define MICROPY_PY_MATH_ATAN2_FIX_INFNAN (1)
+#define MICROPY_PY_MATH_FMOD_FIX_INFNAN (1)
+#ifdef _WIN64
+#define MICROPY_PY_MATH_MODF_FIX_NEGZERO (1)
+#endif
+#endif
 
 // CL specific definitions
 

py/modmath.c

@@ -34,6 +34,8 @@
 // M_PI is not part of the math.h standard and may not be defined
 // And by defining our own we can ensure it uses the correct const format.
 #define MP_PI MICROPY_FLOAT_CONST(3.14159265358979323846)
+#define MP_PI_4 MICROPY_FLOAT_CONST(0.78539816339744830962)
+#define MP_3_PI_4 MICROPY_FLOAT_CONST(2.35619449019234492885)
 
 STATIC NORETURN void math_error(void) {
     mp_raise_ValueError(MP_ERROR_TEXT("math domain error"));
@@ -132,7 +134,17 @@ MATH_FUN_1(asin, asin)
 // atan(x)
 MATH_FUN_1(atan, atan)
 // atan2(y, x)
+#if MICROPY_PY_MATH_ATAN2_FIX_INFNAN
+mp_float_t atan2_func(mp_float_t x, mp_float_t y) {
+    if (isinf(x) && isinf(y)) {
+        return copysign(y < 0 ? MP_3_PI_4 : MP_PI_4, x);
+    }
+    return atan2(x, y);
+}
+MATH_FUN_2(atan2, atan2_func)
+#else
 MATH_FUN_2(atan2, atan2)
+#endif
 // ceil(x)
 MATH_FUN_1_TO_INT(ceil, ceil)
 // copysign(x, y)
@@ -148,7 +160,14 @@ MATH_FUN_1(fabs, fabs_func)
 // floor(x)
 MATH_FUN_1_TO_INT(floor, floor) // TODO: delegate to x.__floor__() if x is not a float
 // fmod(x, y)
+#if MICROPY_PY_MATH_FMOD_FIX_INFNAN
+mp_float_t fmod_func(mp_float_t x, mp_float_t y) {
+    return (!isinf(x) && isinf(y)) ? x : fmod(x, y);
+}
+MATH_FUN_2(fmod, fmod_func)
+#else
 MATH_FUN_2(fmod, fmod)
+#endif
 // isfinite(x)
 MATH_FUN_1_TO_BOOL(isfinite, isfinite)
 // isinf(x)
@@ -246,7 +265,13 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(mp_math_frexp_obj, mp_math_frexp);
 // modf(x)
 STATIC mp_obj_t mp_math_modf(mp_obj_t x_obj) {
     mp_float_t int_part = 0.0;
-    mp_float_t fractional_part = MICROPY_FLOAT_C_FUN(modf)(mp_obj_get_float(x_obj), &int_part);
+    mp_float_t x = mp_obj_get_float(x_obj);
+    mp_float_t fractional_part = MICROPY_FLOAT_C_FUN(modf)(x, &int_part);
+    #if MICROPY_PY_MATH_MODF_FIX_NEGZERO
+    if (fractional_part == MICROPY_FLOAT_CONST(0.0)) {
+        fractional_part = copysign(fractional_part, x);
+    }
+    #endif
     mp_obj_t tuple[2];
     tuple[0] = mp_obj_new_float(fractional_part);
     tuple[1] = mp_obj_new_float(int_part);

py/mpconfig.h

@@ -1128,6 +1128,21 @@ typedef double mp_float_t;
 #define MICROPY_PY_MATH_ISCLOSE (0)
 #endif
 
+// Whether to provide fix for atan2 Inf handling.
+#ifndef MICROPY_PY_MATH_ATAN2_FIX_INFNAN
+#define MICROPY_PY_MATH_ATAN2_FIX_INFNAN (0)
+#endif
+
+// Whether to provide fix for fmod Inf handling.
+#ifndef MICROPY_PY_MATH_FMOD_FIX_INFNAN
+#define MICROPY_PY_MATH_FMOD_FIX_INFNAN (0)
+#endif
+
+// Whether to provide fix for modf negative zero handling.
+#ifndef MICROPY_PY_MATH_MODF_FIX_NEGZERO
+#define MICROPY_PY_MATH_MODF_FIX_NEGZERO (0)
+#endif
+
 // Whether to provide "cmath" module
 #ifndef MICROPY_PY_CMATH
 #define MICROPY_PY_CMATH (0)

tests/float/math_domain.py

@@ -39,8 +39,8 @@ for name, f, args in (
 # double argument functions
 for name, f, args in (
     ("pow", math.pow, ((0, 2), (-1, 2), (0, -1), (-1, 2.3))),
-    ("fmod", math.fmod, ((1.2, inf), (1.2, 0), (inf, 1.2))),
-    ("atan2", math.atan2, ((0, 0),)),
+    ("fmod", math.fmod, ((1.2, inf), (1.2, -inf), (1.2, 0), (inf, 1.2))),
+    ("atan2", math.atan2, ((0, 0), (-inf, inf), (-inf, -inf), (inf, -inf))),
     ("copysign", math.copysign, ()),
 ):
     for x in args + ((0, inf), (inf, 0), (inf, inf), (inf, nan), (nan, inf), (nan, nan)):