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libjit/jit/jit-varint.c  view on Meta::CPAN

/*
 * jit-varint.c - Variable length integer encoding.
 *
 * Copyright (C) 2011  Aleksey Demakov
 *
 * The libjit library is free software: you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation, either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * The libjit library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with the libjit library.  If not, see
 * <http://www.gnu.org/licenses/>.
 */

#include <jit/jit.h>
#include "jit-varint.h"

/*
 * Flush the current encode buffer.
 */
static int
flush_encoder(jit_varint_encoder_t *encoder)
{
	jit_varint_data_t data;

	/* Allocate a new jit_varint_data structure to hold the data */
	data = jit_malloc(sizeof(struct jit_varint_data) + encoder->len);
	if(!data)
	{
		return 0;
	}

	/* Copy the temporary debug data into the new structure */
	jit_memcpy(data->data, encoder->buf, encoder->len);

	/* Link the structure into the debug list */
	data->next = 0;
	if(encoder->last)
	{
		encoder->last->next = data;
	}
	else
	{
		encoder->data = data;
	}
	encoder->last = data;

	/* Reset the temporary debug buffer */
	encoder->len = 0;
	return 1;
}

void
_jit_varint_init_encoder(jit_varint_encoder_t *encoder)
{
	encoder->len = 0;
	encoder->data = 0;
	encoder->last = 0;
}

void
_jit_varint_init_decoder(jit_varint_decoder_t *decoder, jit_varint_data_t data)
{
	decoder->len = 0;
	decoder->data = data;
	decoder->end = (data == 0);
}

int
_jit_varint_encode_end(jit_varint_encoder_t *encoder)
{
	if(!encoder->len)
	{
		return 1;
	}

	/* Mark the end of the data */
	encoder->buf[encoder->len++] = 0xFF;

	/* Flush the data that we have collected so far */
	return flush_encoder(encoder);
}

/*
 * Compress a "long" value so that it takes up less bytes.
 * This is used to store offsets within functions and
 * debug line numbers, which are usually small integers.
 */
int
_jit_varint_encode_uint(jit_varint_encoder_t *encoder, jit_uint value)
{
	if(encoder->len + 6 > sizeof(encoder->buf))
	{
		/* Overflow occurred: end current buffer */
		if(!_jit_varint_encode_end(encoder))
		{
			return 0;
		}
	}

	/* Write the value to the temporary buffer */
	if(value < 0x80)
	{
		/* 0xxx xxxx */
		encoder->buf[encoder->len++] = (unsigned char) (value);
	}
	else if(value < 0x4000)
	{
		/* 10xx xxxx | xxxx xxxx */
		encoder->buf[encoder->len++] = (unsigned char) (value >> 8) | 0x80;
		encoder->buf[encoder->len++] = (unsigned char) (value);
	}
	else if(value < 0x200000)
	{
		/* 110x xxxx | xxxx xxxx | xxxx xxxx */
		encoder->buf[encoder->len++] = (unsigned char) (value >> 16) | 0xC0;
		encoder->buf[encoder->len++] = (unsigned char) (value >> 8);
		encoder->buf[encoder->len++] = (unsigned char) (value);
	}
	else if(value < 0x10000000)
	{
		/* 1110 xxxx | xxxx xxxx | xxxx xxxx | xxxx xxxx */
		encoder->buf[encoder->len++] = (unsigned char) (value >> 24) | 0xE0;
		encoder->buf[encoder->len++] = (unsigned char) (value >> 16);
		encoder->buf[encoder->len++] = (unsigned char) (value >> 8);
		encoder->buf[encoder->len++] = (unsigned char) (value);
	}
	else
	{
		/* 1111 0000 | xxxx xxxx | xxxx xxxx | xxxx xxxx | xxxx xxxx */
		encoder->buf[encoder->len++] = 0xF0;
		encoder->buf[encoder->len++] = (unsigned char) (value >> 24);
		encoder->buf[encoder->len++] = (unsigned char) (value >> 16);
		encoder->buf[encoder->len++] = (unsigned char) (value >> 8);
		encoder->buf[encoder->len++] = (unsigned char) (value);
	}

	return 1;
}

jit_varint_data_t
_jit_varint_get_data(jit_varint_encoder_t *encoder)
{
	return encoder->data;
}

void