path: root/libsyscalls_parse_signed_integer.c

/* See LICENSE file for copyright and license details. */
#include "common.h"


enum libsyscalls_error
libsyscalls_parse_signed_integer(unsigned long long int value_in, enum libsyscalls_datatype_sign_representation representation,
                                 size_t bits, unsigned long long int *value_out, int *negative_out)
{
	unsigned long long int value = value_in, mask;
	int negative = 0;

	if (!bits || bits > sizeof(value) / sizeof(char) * CHAR_BIT)
		return LIBSYSCALLS_E_INVAL;

	switch (representation) {
	case LIBSYSCALLS_SIGN_UNDETERMINED:
		break;

	case LIBSYSCALLS_SIGN_TWOS_COMPLEMENT:
		if (value >> (bits - 1U)) {
			mask = (1ULL << (bits - 1U)) - 1ULL;
			value = ~value & mask;
			value += 1ULL;
			negative = 1;
		}
		break;

	case LIBSYSCALLS_SIGN_ONES_COMPLEMENT:
		if (value >> (bits - 1U)) {
			mask = (1ULL << (bits - 1U)) - 1ULL;
			value = ~value & mask;
			negative = 1;
		}
		break;

	case LIBSYSCALLS_SIGN_SIGN_MAGNITUDE:
		if (value >> (bits - 1U)) {
			value ^= 1ULL << (bits - 1U);
			negative = 1;
		}
		break;

	case LIBSYSCALLS_SIGN_EXCESS_HALF:
		if (value >> (bits - 1U)) {
			value ^= 1ULL << (bits - 1U);
		} else {
			value = (1ULL << (bits - 1U)) - value;
			negative = 1;
		}
		break;

	default:
		return LIBSYSCALLS_E_INVAL;
	}

	if (value_out)
		*value_out = value;
	if (negative_out)
		*negative_out = negative;
	return LIBSYSCALLS_E_OK;
}