py/modmath: Make MICROPY_PY_MATH_POW_FIX_NAN also fix pow(x, NaN) cases.

This is needed by the zephyr port.  Combining it with the existing
`MICROPY_PY_MATH_POW_FIX_NAN` option should be safe, and eliminates the
need for a separate option.

Signed-off-by: Damien George <damien@micropython.org>

py/modmath.c

@@ -99,12 +99,16 @@ mp_float_t MICROPY_FLOAT_C_FUN(log2)(mp_float_t x) {
 MATH_FUN_1(sqrt, sqrt)
 // pow(x, y): returns x to the power of y
 #if MICROPY_PY_MATH_POW_FIX_NAN
-mp_float_t pow_func(mp_float_t x, mp_float_t y) {
+mp_float_t MICROPY_FLOAT_C_FUN(pow_func)(mp_float_t x, mp_float_t y) {
     // pow(base, 0) returns 1 for any base, even when base is NaN
     // pow(+1, exponent) returns 1 for any exponent, even when exponent is NaN
     if (x == MICROPY_FLOAT_CONST(1.0) || y == MICROPY_FLOAT_CONST(0.0)) {
         return MICROPY_FLOAT_CONST(1.0);
     }
+    // pow(base, NaN) returns NaN for any other value of base
+    if (isnan(y)) {
+        return y;
+    }
     return MICROPY_FLOAT_C_FUN(pow)(x, y);
 }
 MATH_FUN_2(pow, pow_func)

py/mpconfig.h

@@ -1559,6 +1559,7 @@ typedef time_t mp_timestamp_t;
 #endif
 
 // Whether to provide fix for pow(1, NaN) and pow(NaN, 0), which both should be 1 not NaN.
+// Also fixes pow(base, NaN) to return NaN for other values of base.
 #ifndef MICROPY_PY_MATH_POW_FIX_NAN
 #define MICROPY_PY_MATH_POW_FIX_NAN (0)
 #endif

py/objfloat.c

@@ -301,6 +301,10 @@ mp_obj_t mp_obj_float_binary_op(mp_binary_op_t op, mp_float_t lhs_val, mp_obj_t
                 lhs_val = MICROPY_FLOAT_CONST(1.0);
                 break;
             }
+            if (isnan(rhs_val)) {
+                lhs_val = rhs_val;
+                break;
+            }
             #endif
             lhs_val = MICROPY_FLOAT_C_FUN(pow)(lhs_val, rhs_val);
             break;