py: Implement divmod, % and proper // for floating point.

Tested and working on unix and pyboard.

lib/libm/fmodf.c

+/*****************************************************************************/
+/*****************************************************************************/
+// fmodf from musl-0.9.15
+/*****************************************************************************/
+/*****************************************************************************/
+
+#include "libm.h"
+
+float fmodf(float x, float y)
+{
+	union {float f; uint32_t i;} ux = {x}, uy = {y};
+	int ex = ux.i>>23 & 0xff;
+	int ey = uy.i>>23 & 0xff;
+	uint32_t sx = ux.i & 0x80000000;
+	uint32_t i;
+	uint32_t uxi = ux.i;
+
+	if (uy.i<<1 == 0 || isnan(y) || ex == 0xff)
+		return (x*y)/(x*y);
+	if (uxi<<1 <= uy.i<<1) {
+		if (uxi<<1 == uy.i<<1)
+			return 0*x;
+		return x;
+	}
+
+	/* normalize x and y */
+	if (!ex) {
+		for (i = uxi<<9; i>>31 == 0; ex--, i <<= 1);
+		uxi <<= -ex + 1;
+	} else {
+		uxi &= -1U >> 9;
+		uxi |= 1U << 23;
+	}
+	if (!ey) {
+		for (i = uy.i<<9; i>>31 == 0; ey--, i <<= 1);
+		uy.i <<= -ey + 1;
+	} else {
+		uy.i &= -1U >> 9;
+		uy.i |= 1U << 23;
+	}
+
+	/* x mod y */
+	for (; ex > ey; ex--) {
+		i = uxi - uy.i;
+		if (i >> 31 == 0) {
+			if (i == 0)
+				return 0*x;
+			uxi = i;
+		}
+		uxi <<= 1;
+	}
+	i = uxi - uy.i;
+	if (i >> 31 == 0) {
+		if (i == 0)
+			return 0*x;
+		uxi = i;
+	}
+	for (; uxi>>23 == 0; uxi <<= 1, ex--);
+
+	/* scale result up */
+	if (ex > 0) {
+		uxi -= 1U << 23;
+		uxi |= (uint32_t)ex << 23;
+	} else {
+		uxi >>= -ex + 1;
+	}
+	uxi |= sx;
+	ux.i = uxi;
+	return ux.f;
+}

lib/libm/math.c

@@ -117,7 +117,6 @@ float acoshf(float x) { return 0.0; }
 float asinhf(float x) { return 0.0; }
 float atanhf(float x) { return 0.0; }
 float tanf(float x) { return 0.0; }
-float fmodf(float x, float y) { return 0.0; }
 float tgammaf(float x) { return 0.0; }
 float lgammaf(float x) { return 0.0; }
 float erff(float x) { return 0.0; }

py/builtin.c

@@ -242,13 +242,32 @@ STATIC mp_obj_t mp_builtin_dir(mp_uint_t n_args, const mp_obj_t *args) {
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_dir_obj, 0, 1, mp_builtin_dir);
 
 STATIC mp_obj_t mp_builtin_divmod(mp_obj_t o1_in, mp_obj_t o2_in) {
+    // TODO handle big int
     if (MP_OBJ_IS_SMALL_INT(o1_in) && MP_OBJ_IS_SMALL_INT(o2_in)) {
         mp_int_t i1 = MP_OBJ_SMALL_INT_VALUE(o1_in);
         mp_int_t i2 = MP_OBJ_SMALL_INT_VALUE(o2_in);
+        if (i2 == 0) {
+            zero_division_error:
+            nlr_raise(mp_obj_new_exception_msg(&mp_type_ZeroDivisionError, "division by zero"));
+        }
         mp_obj_t args[2];
         args[0] = MP_OBJ_NEW_SMALL_INT(i1 / i2);
         args[1] = MP_OBJ_NEW_SMALL_INT(i1 % i2);
         return mp_obj_new_tuple(2, args);
+#if MICROPY_PY_BUILTINS_FLOAT
+    } else if (MP_OBJ_IS_TYPE(o1_in, &mp_type_float) || MP_OBJ_IS_TYPE(o2_in, &mp_type_float)) {
+        mp_float_t f1 = mp_obj_get_float(o1_in);
+        mp_float_t f2 = mp_obj_get_float(o2_in);
+        if (f2 == 0.0) {
+            goto zero_division_error;
+        }
+        mp_obj_float_divmod(&f1, &f2);
+        mp_obj_t tuple[2] = {
+            mp_obj_new_float(f1),
+            mp_obj_new_float(f2),
+        };
+        return mp_obj_new_tuple(2, tuple);
+#endif
     } else {
         nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "unsupported operand type(s) for divmod(): '%s' and '%s'", mp_obj_get_type_str(o1_in), mp_obj_get_type_str(o2_in)));
     }

py/obj.h

@@ -487,6 +487,7 @@ typedef struct _mp_obj_float_t {
 } mp_obj_float_t;
 mp_float_t mp_obj_float_get(mp_obj_t self_in);
 mp_obj_t mp_obj_float_binary_op(mp_uint_t op, mp_float_t lhs_val, mp_obj_t rhs); // can return MP_OBJ_NULL if op not supported
+void mp_obj_float_divmod(mp_float_t *x, mp_float_t *y);
 
 // complex
 void mp_obj_complex_get(mp_obj_t self_in, mp_float_t *real, mp_float_t *imag);

py/objfloat.c

@@ -143,14 +143,16 @@ mp_obj_t mp_obj_float_binary_op(mp_uint_t op, mp_float_t lhs_val, mp_obj_t rhs_i
         case MP_BINARY_OP_INPLACE_SUBTRACT: lhs_val -= rhs_val; break;
         case MP_BINARY_OP_MULTIPLY:
         case MP_BINARY_OP_INPLACE_MULTIPLY: lhs_val *= rhs_val; break;
-        // TODO: verify that C floor matches Python semantics
         case MP_BINARY_OP_FLOOR_DIVIDE:
         case MP_BINARY_OP_INPLACE_FLOOR_DIVIDE:
             if (rhs_val == 0) {
                 zero_division_error:
-                nlr_raise(mp_obj_new_exception_msg(&mp_type_ZeroDivisionError, "float division by zero"));
+                nlr_raise(mp_obj_new_exception_msg(&mp_type_ZeroDivisionError, "division by zero"));
             }
-            lhs_val = MICROPY_FLOAT_C_FUN(floor)(lhs_val / rhs_val);
+            // Python specs require that x == (x//y)*y + (x%y) so we must
+            // call divmod to compute the correct floor division, which
+            // returns the floor divide in lhs_val.
+            mp_obj_float_divmod(&lhs_val, &rhs_val);
             break;
         case MP_BINARY_OP_TRUE_DIVIDE:
         case MP_BINARY_OP_INPLACE_TRUE_DIVIDE:
@@ -159,6 +161,21 @@ mp_obj_t mp_obj_float_binary_op(mp_uint_t op, mp_float_t lhs_val, mp_obj_t rhs_i
             }
             lhs_val /= rhs_val;
             break;
+        case MP_BINARY_OP_MODULO:
+        case MP_BINARY_OP_INPLACE_MODULO:
+            if (rhs_val == 0) {
+                goto zero_division_error;
+            }
+            lhs_val = MICROPY_FLOAT_C_FUN(fmod)(lhs_val, rhs_val);
+            // Python specs require that mod has same sign as second operand
+            if (lhs_val == 0.0) {
+                lhs_val = MICROPY_FLOAT_C_FUN(copysign)(0.0, rhs_val);
+            } else {
+                if ((lhs_val < 0.0) != (rhs_val < 0.0)) {
+                    lhs_val += rhs_val;
+                }
+            }
+            break;
         case MP_BINARY_OP_POWER:
         case MP_BINARY_OP_INPLACE_POWER: lhs_val = MICROPY_FLOAT_C_FUN(pow)(lhs_val, rhs_val); break;
         case MP_BINARY_OP_LESS: return MP_BOOL(lhs_val < rhs_val);
@@ -173,4 +190,39 @@ mp_obj_t mp_obj_float_binary_op(mp_uint_t op, mp_float_t lhs_val, mp_obj_t rhs_i
     return mp_obj_new_float(lhs_val);
 }
 
+void mp_obj_float_divmod(mp_float_t *x, mp_float_t *y) {
+    // logic here follows that of CPython
+    // https://docs.python.org/3/reference/expressions.html#binary-arithmetic-operations
+    // x == (x//y)*y + (x%y)
+    // divmod(x, y) == (x//y, x%y)
+    mp_float_t mod = MICROPY_FLOAT_C_FUN(fmod)(*x, *y);
+    mp_float_t div = (*x - mod) / *y;
+
+    // Python specs require that mod has same sign as second operand
+    if (mod == 0.0) {
+        mod = MICROPY_FLOAT_C_FUN(copysign)(0.0, *y);
+    } else {
+        if ((mod < 0.0) != (*y < 0.0)) {
+            mod += *y;
+            div -= 1.0;
+        }
+    }
+
+    mp_float_t floordiv;
+    if (div == 0.0) {
+        // if division is zero, take the correct sign of zero
+        floordiv = MICROPY_FLOAT_C_FUN(copysign)(0.0, *x / *y);
+    } else {
+        // Python specs require that x == (x//y)*y + (x%y)
+        floordiv = MICROPY_FLOAT_C_FUN(floor)(div);
+        if (div - floordiv > 0.5) {
+            floordiv += 1.0;
+        }
+    }
+
+    // return results
+    *x = floordiv;
+    *y = mod;
+}
+
 #endif // MICROPY_PY_BUILTINS_FLOAT

stmhal/Makefile

@@ -67,6 +67,7 @@ SRC_LIB = $(addprefix lib/,\
 	libm/asinfacosf.c \
 	libm/atanf.c \
 	libm/atan2f.c \
+	libm/fmodf.c \
 	)
 
 SRC_C = \

tests/float/modulo.py

-# check modulo matches python definition
-# TODO we currenty fail with this
-if False:
-	print(1.23456 % 0.7)
-	print(-1.23456 % 0.7)
-	print(1.23456 % -0.7)
-	print(-1.23456 % -0.7)
-
-	a = 1.23456
-	b = 0.7
-	print(a % b)
-	print(a % -b)
-	print(-a % b)
-	print(-a % -b)

tests/run-tests

@@ -33,6 +33,10 @@ def run_tests(pyb, tests, args):
     if os.getenv('TRAVIS') == 'true':
         skip_tests.add('basics/memoryerror.py')
 
+    # Some tests shouldn't be run on pyboard
+    if pyb is not None:
+        skip_tests.add('float/float_divmod.py') # tested by float/float_divmod_relaxed.py instead
+
     # Some tests are known to fail with native emitter
     # Remove them from the below when they work
     if args.emit == 'native':