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diff --git a/circuitpython/py/smallint.h b/circuitpython/py/smallint.h
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+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * SPDX-FileCopyrightText: Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_PY_SMALLINT_H
+#define MICROPY_INCLUDED_PY_SMALLINT_H
+
+#include "py/mpconfig.h"
+#include "py/misc.h"
+
+// Functions for small integer arithmetic
+
+#ifndef MP_SMALL_INT_MIN
+
+// In SMALL_INT, next-to-highest bits is used as sign, so both must match for value in range
+#if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_A || MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_C
+
+#define MP_SMALL_INT_MIN ((mp_int_t)(((mp_int_t)MP_OBJ_WORD_MSBIT_HIGH) >> 1))
+#define MP_SMALL_INT_FITS(n) ((((n) ^ ((mp_uint_t)(n) << 1)) & MP_OBJ_WORD_MSBIT_HIGH) == 0)
+// Mask to truncate mp_int_t to positive value
+#define MP_SMALL_INT_POSITIVE_MASK ~(MP_OBJ_WORD_MSBIT_HIGH | (MP_OBJ_WORD_MSBIT_HIGH >> 1))
+
+#elif MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_B
+
+#define MP_SMALL_INT_MIN ((mp_int_t)(((mp_int_t)MP_OBJ_WORD_MSBIT_HIGH) >> 2))
+#define MP_SMALL_INT_FITS(n) ((((n) & MP_SMALL_INT_MIN) == 0) || (((n) & MP_SMALL_INT_MIN) == MP_SMALL_INT_MIN))
+// Mask to truncate mp_int_t to positive value
+#define MP_SMALL_INT_POSITIVE_MASK ~(MP_OBJ_WORD_MSBIT_HIGH | (MP_OBJ_WORD_MSBIT_HIGH >> 1) | (MP_OBJ_WORD_MSBIT_HIGH >> 2))
+
+#elif MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_D
+
+#define MP_SMALL_INT_MIN ((mp_int_t)(((mp_int_t)0xffff800000000000) >> 1))
+#define MP_SMALL_INT_FITS(n) ((((n) ^ ((n) << 1)) & 0xffff800000000000) == 0)
+// Mask to truncate mp_int_t to positive value
+#define MP_SMALL_INT_POSITIVE_MASK ~(0xffff800000000000 | (0xffff800000000000 >> 1))
+
+#endif
+
+#endif
+
+#define MP_SMALL_INT_MAX ((mp_int_t)(~(MP_SMALL_INT_MIN)))
+
+bool mp_small_int_mul_overflow(mp_int_t x, mp_int_t y);
+mp_int_t mp_small_int_modulo(mp_int_t dividend, mp_int_t divisor);
+mp_int_t mp_small_int_floor_divide(mp_int_t num, mp_int_t denom);
+
+#endif // MICROPY_INCLUDED_PY_SMALLINT_H