Build everything as C++ (#1176)

src/opmath.cpp

@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: MIT */
+
+// Mathematical operators that don't reuse C's behavior
+
+#include <stdint.h>
+
+#include "opmath.hpp"
+
+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;
+}
+
+int32_t op_shift_right_unsigned(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);
+
+	return (uint32_t)value >> amount;
+}