Function psl_a85_encode

src/postscriptlight.c:1159–1238

}

static size_t psl_a85_encode (struct PSL_CTRL *PSL, const unsigned char *src_buf, size_t nbytes) {
	/* Encode 4-byte binary data from src_buf to 5-byte ASCII85
	 * Special cases: 0x00000000 is encoded as z
	 * Encoded data is stored in dst_buf and written to file in
	 * one go, which is faster than writing one char at a time.
	 * The function returns the output buffer size. */
	size_t dst_buf_size;
	unsigned char *dst_buf, *dst_ptr;
	const unsigned char *src_ptr = src_buf, *src_end = src_buf + nbytes;
	const unsigned int max_line_len = 95; /* number of chars after which a newline is inserted */

	if (!nbytes)
		/* Ignore empty input */
		return 0;

	/* dst_buf has to be large enough to hold data + line endings */
	dst_buf_size = (size_t)(nbytes * 1.25 + 1);      /* output buffer is at least 1.25 times larger */
	dst_buf_size += dst_buf_size / max_line_len + 4; /* add more space for '\n' and delimiter */
	dst_ptr = dst_buf = PSL_memory (PSL, NULL, dst_buf_size, unsigned char); /* output buffer */

	do { /* for each quad in src_buf while src_ptr < src_end */
		const size_t ilen = nbytes > 4 ? 4 : nbytes, olen = ilen + 1;
		static unsigned int line_len = 0;
		unsigned int i, n = 0, byte;
		int j;
		unsigned char quintuple[5] = { 0 };

		/* Wrap 4 chars into a 4-byte integer */
		for (i = 0; i < ilen; ++i) {
			byte = *src_ptr++;
			n += byte << (24 - 8*i);
		}

		if (n == 0 && ilen == 4) {
			/* Set the only output byte to "z" */
			*dst_ptr++ = 'z';
			++line_len;
			continue;
		}

		/* Else determine output 5-tuple */
		for (j = 4; j >= 0; --j) {
			quintuple[j] = (unsigned char) ((n % 85) + '!');
			n = n / 85;
		}

		/* Copy olen bytes to dst_buf */
		memcpy (dst_ptr, quintuple, olen);
		line_len += (unsigned int)olen;
		dst_ptr += olen;

		/* Insert newline when line exceeds 95 characters */
		if (line_len + 1 > max_line_len) {
			*dst_ptr++ = '\n';
			line_len = 0;
		}
	} while (nbytes -= 4, src_ptr < src_end); /* end do */