/* ************************************************************************** */
/*                                       _____           _                    */
/*  utils/skip.c                        |_   _|__  _   _| |__   ___ _   _     */
/*  | Project: libg1m                     | |/ _ \| | | | '_ \ / _ \ | | |    */
/*                                        | | (_) | |_| | | | |  __/ |_| |    */
/*  By: thomas <thomas@touhey.fr>         |_|\___/ \__,_|_| |_|\___|\__, |.fr */
/*  Last updated: 2016/12/01 13:33:41                               |___/     */
/*                                                                            */
/* ************************************************************************** */
#include <libg1m/internals.h>

/**
 *	g1m_parse_skip:
 *	Skip some bytes.
 *
 *	I've made two loops to avoid conditions in each loop iteration
 *	when checksum is not calculated.
 *
 *	@arg	stream		the stream where to skip bytes.
 *	@arg	size		the size to skip.
 *	@arg	checksum	pointer to the checksum variable if there is one.
 */

int g1m_parse_skip(FILE *stream, size_t size, uint_fast32_t *checksum)
{
	uint8_t buf[1024];
#if LOGLEVEL <= ll_error
	size_t size_ini = size;
#endif

	if (checksum) {
		uint_fast32_t add = 0;
		while (1) {
			/* if no size left, exit */
			if (!size) break;

			/* read that much */
			{
				size_t curlen = min(size, 1024);
				size_t read_len = fread(buf, 1, curlen, stream);
				size -= read_len;
				if (read_len < curlen) {
					log_error("SKIPPING failed, skipped "
						"%" PRIuSIZE "/%" PRIuSIZE " bytes, "
						"%" PRIuSIZE " missing",
						size_ini - size, size_ini, size);
					return (g1m_error_eof);
				}

				/* feed the checksum */
				add = g1m_checksum32(buf, curlen, add);
			}
		}
		*checksum += add;
	} else {
		while (1) {
			/* if no size left, exit */
			if (!size) break;

			/* read that much */
			{
				size_t curlen = min(size, 1024);
				size_t read_len = fread(buf, 1, curlen, stream);
				size -= read_len;
				if (read_len < curlen) {
					log_error("SKIPPING failed, skipped "
						"%" PRIuSIZE "/%" PRIuSIZE " bytes, "
						"%" PRIuSIZE " missing",
						size_ini - size, size_ini, size);
					return (g1m_error_eof);
				}
			}
		}
	}

	/* no error */
	return (0);
}