From bdc6e86e079dd8a82e9ead1d4041c2e17c882437 Mon Sep 17 00:00:00 2001
From: Damien George
Date: Tue, 26 Sep 2017 12:57:51 +1000
Subject: py/objfloat: Support raising a negative number to a fractional power.

This returns a complex number, following CPython behaviour.  For ports that
don't have complex numbers enabled this will raise a ValueError which gives
a fail-safe for scripts that were written assuming complex numbers exist.
---
 py/objfloat.c | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'py/objfloat.c')

diff --git a/py/objfloat.c b/py/objfloat.c
index 55a9379ff..0831be3fd 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -298,6 +298,13 @@ mp_obj_t mp_obj_float_binary_op(mp_binary_op_t op, mp_float_t lhs_val, mp_obj_t
             if (lhs_val == 0 && rhs_val < 0) {
                 goto zero_division_error;
             }
+            if (lhs_val < 0 && rhs_val != MICROPY_FLOAT_C_FUN(floor)(rhs_val)) {
+                #if MICROPY_PY_BUILTINS_COMPLEX
+                return mp_obj_complex_binary_op(MP_BINARY_OP_POWER, lhs_val, 0, rhs_in);
+                #else
+                mp_raise_ValueError("complex values not supported");
+                #endif
+            }
             lhs_val = MICROPY_FLOAT_C_FUN(pow)(lhs_val, rhs_val);
             break;
         case MP_BINARY_OP_DIVMOD: {
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