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/*
* Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#ifndef OSSL_INTERNAL_QUIC_VLINT_H
# define OSSL_INTERNAL_QUIC_VLINT_H
# pragma once
#include "internal/e_os.h"
/* The smallest value requiring a 1, 2, 4, or 8-byte representation. */
#define OSSL_QUIC_VLINT_1B_MIN 0
#define OSSL_QUIC_VLINT_2B_MIN 64
#define OSSL_QUIC_VLINT_4B_MIN 16384
#define OSSL_QUIC_VLINT_8B_MIN 1073741824
/* The largest value representable in a given number of bytes. */
#define OSSL_QUIC_VLINT_1B_MAX (OSSL_QUIC_VLINT_2B_MIN - 1)
#define OSSL_QUIC_VLINT_2B_MAX (OSSL_QUIC_VLINT_4B_MIN - 1)
#define OSSL_QUIC_VLINT_4B_MAX (OSSL_QUIC_VLINT_8B_MIN - 1)
#define OSSL_QUIC_VLINT_8B_MAX (((uint64_t)1 << 62) - 1)
/* The largest value representable as a variable-length integer. */
#define OSSL_QUIC_VLINT_MAX OSSL_QUIC_VLINT_8B_MAX
/*
* Returns the number of bytes needed to encode v in the QUIC variable-length
* integer encoding.
*
* Returns 0 if v exceeds OSSL_QUIC_VLINT_MAX.
*/
static ossl_unused ossl_inline size_t ossl_quic_vlint_encode_len(uint64_t v)
{
if (v < OSSL_QUIC_VLINT_2B_MIN)
return 1;
if (v < OSSL_QUIC_VLINT_4B_MIN)
return 2;
if (v < OSSL_QUIC_VLINT_8B_MIN)
return 4;
if (v <= OSSL_QUIC_VLINT_MAX)
return 8;
return 0;
}
/*
* This function writes a QUIC varable-length encoded integer to buf.
* The smallest usable representation is used.
*
* It is the caller's responsibility to ensure that the buffer is big enough by
* calling ossl_quic_vlint_encode_len(v) before calling this function.
*
* Precondition: buf is at least ossl_quic_vlint_enc_len(v) bytes in size
* (unchecked)
* Precondition: v does not exceed OSSL_QUIC_VLINT_MAX
* (unchecked)
*/
void ossl_quic_vlint_encode(unsigned char *buf, uint64_t v);
/*
* This function writes a QUIC variable-length encoded integer to buf. The
* specified number of bytes n are used for the encoding, which means that the
* encoded value may take up more space than necessary.
*
* It is the caller's responsibility to ensure that the buffer is of at least n
* bytes, and that v is representable by a n-byte QUIC variable-length integer.
* The representable ranges are:
*
* 1-byte encoding: [0, 2** 6-1]
* 2-byte encoding: [0, 2**14-1]
* 4-byte encoding: [0, 2**30-1]
* 8-byte encoding: [0, 2**62-1]
*
* Precondition: buf is at least n bytes in size (unchecked)
* Precondition: v does not exceed the representable range
* (ossl_quic_vlint_encode_len(v) <= n) (unchecked)
* Precondition: v does not exceed OSSL_QUIC_VLINT_MAX
* (unchecked)
*/
void ossl_quic_vlint_encode_n(unsigned char *buf, uint64_t v, int n);
/*
* Given the first byte of an encoded QUIC variable-length integer, returns
* the number of bytes comprising the encoded integer, including the first
* byte.
*/
static ossl_unused ossl_inline size_t ossl_quic_vlint_decode_len(uint8_t first_byte)
{
return 1U << ((first_byte & 0xC0) >> 6);
}
/*
* Given a buffer containing an encoded QUIC variable-length integer, returns
* the decoded value. The buffer must be of at least
* ossl_quic_vlint_decode_len(buf[0]) bytes in size, and the caller is responsible
* for checking this.
*
* Precondition: buf is at least ossl_quic_vlint_decode_len(buf[0]) bytes in size
* (unchecked)
*/
uint64_t ossl_quic_vlint_decode_unchecked(const unsigned char *buf);
/*
* Given a buffer buf of buf_len bytes in length, attempts to decode an encoded
* QUIC variable-length integer at the start of the buffer and writes the result
* to *v. If buf_len is inadequate, suggesting a truncated encoded integer, the
* function fails and 0 is returned. Otherwise, returns the number of bytes
* consumed.
*
* Precondition: buf is at least buf_len bytes in size
* Precondition: v (unchecked)
*/
int ossl_quic_vlint_decode(const unsigned char *buf, size_t buf_len, uint64_t *v);
#endif
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