libsyscalls_make_signed_integer.c


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


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

	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 (negative && value) {
			highbit = 1ULL << (bits - 1U);
			mask = highbit - 1ULL;
			value = ~(value - 1) & mask;
			value |= highbit;
		}
		break;

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

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

	case LIBSYSCALLS_SIGN_EXCESS_HALF:
		if (!negative)
			value ^= 1ULL << (bits - 1);
		else
			value = (1ULL << (bits - 1)) - value;
		break;

	default:
		return LIBSYSCALLS_E_INVAL;
	}

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