ref: 69d7f845025dfcc3017e58453273be46a0107993
dir: /src/opmath.c/
/* * This file is part of RGBDS. * * Copyright (c) 1997-2021, RGBDS contributors. * * SPDX-License-Identifier: MIT */ /* * Mathematical operators that don't reuse C's behavior */ #include <stdint.h> #include "opmath.h" int32_t op_divide(int32_t dividend, int32_t divisor) { // Adjust division to floor toward negative infinity, // not truncate toward zero return dividend / divisor - ((dividend % divisor < 0) != (divisor < 0)); } int32_t op_modulo(int32_t dividend, int32_t divisor) { int32_t remainder = dividend % divisor; // Adjust modulo to have the sign of the divisor, // not the sign of the dividend return remainder + divisor * ((remainder < 0) != (divisor < 0)); } int32_t op_exponent(int32_t base, uint32_t power) { int32_t result = 1; for (;;) { if (power % 2) result *= base; power /= 2; if (!power) break; base *= base; } return result; } int32_t op_shift_left(int32_t value, int32_t amount) { // Get the easy cases out of the way if (amount == 0) return value; if (value == 0 || amount >= 32) return 0; if (amount < -31) return (value < 0) ? -1 : 0; if (amount < 0) return op_shift_right(value, -amount); // Use unsigned to force a bitwise shift // Casting back is OK because the types implement two's complement behavior return (uint32_t)value << amount; } int32_t op_shift_right(int32_t value, int32_t amount) { // Repeat the easy cases here to avoid INT_MIN funny business if (amount == 0) return value; if (value == 0 || amount <= -32) return 0; if (amount > 31) return (value < 0) ? -1 : 0; if (amount < 0) return op_shift_left(value, -amount); if (value > 0) return (uint32_t)value >> amount; // Calculate an OR mask for sign extension // 1->0x80000000, 2->0xC0000000, ..., 31->0xFFFFFFFE uint32_t amount_high_bits = -(UINT32_C(1) << (32 - amount)); // The C standard leaves shifting right negative values // undefined, so use a left shift manually sign-extended return ((uint32_t)value >> amount) | amount_high_bits; }