src/core/lib/transport/chttp2/varint.h

/*
 *
 * Copyright 2015-2016, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 */

#ifndef GRPC_CORE_LIB_TRANSPORT_CHTTP2_VARINT_H
#define GRPC_CORE_LIB_TRANSPORT_CHTTP2_VARINT_H

#include <grpc/support/port_platform.h>

/* Helpers for hpack varint encoding */

/* length of a value that needs varint tail encoding (it's bigger than can be
   bitpacked into the opcode byte) - returned value includes the length of the
   opcode byte */
uint32_t grpc_chttp2_hpack_varint_length(uint32_t tail_value);

void grpc_chttp2_hpack_write_varint_tail(uint32_t tail_value, uint8_t* target,
                                         uint32_t tail_length);

/* maximum value that can be bitpacked with the opcode if the opcode has a
   prefix
   of length prefix_bits */
#define GRPC_CHTTP2_MAX_IN_PREFIX(prefix_bits) \
  ((uint32_t)((1 << (8 - (prefix_bits))) - 1))

/* length required to bitpack a value */
#define GRPC_CHTTP2_VARINT_LENGTH(n, prefix_bits) \
  ((n) < GRPC_CHTTP2_MAX_IN_PREFIX(prefix_bits)   \
       ? 1u                                       \
       : grpc_chttp2_hpack_varint_length(         \
             (n)-GRPC_CHTTP2_MAX_IN_PREFIX(prefix_bits)))

#define GRPC_CHTTP2_WRITE_VARINT(n, prefix_bits, prefix_or, target, length)   \
  do {                                                                        \
    uint8_t* tgt = target;                                                    \
    if ((length) == 1u) {                                                     \
      (tgt)[0] = (uint8_t)((prefix_or) | (n));                                \
    } else {                                                                  \
      (tgt)[0] =                                                              \
          (prefix_or) | (uint8_t)GRPC_CHTTP2_MAX_IN_PREFIX(prefix_bits);      \
      grpc_chttp2_hpack_write_varint_tail(                                    \
          (n)-GRPC_CHTTP2_MAX_IN_PREFIX(prefix_bits), (tgt) + 1, (length)-1); \
    }                                                                         \
  } while (0)

#endif /* GRPC_CORE_LIB_TRANSPORT_CHTTP2_VARINT_H */