lzlib/cbuffer.c

/* Lzlib - Compression library for the lzip format
   Copyright (C) 2009-2025 Antonio Diaz Diaz.

   This library is free software. Redistribution and use in source and
   binary forms, with or without modification, are permitted provided
   that the following conditions are met:

   1. Redistributions of source code must retain the above copyright
   notice, this list of conditions, and the following disclaimer.

   2. 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.

   This 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.
*/

typedef struct Circular_buffer
  {
  uint8_t * buffer;
  unsigned buffer_size;		/* capacity == buffer_size - 1 */
  unsigned get;			/* buffer is empty when get == put */
  unsigned put;
  } Circular_buffer;

static inline bool Cb_init( Circular_buffer * const cb,
                            const unsigned buf_size )
  {
  cb->buffer_size = buf_size + 1;
  cb->get = 0;
  cb->put = 0;
  cb->buffer =
    ( cb->buffer_size > 1 ) ? (uint8_t *)malloc( cb->buffer_size ) : 0;
  return cb->buffer != 0;
  }

static inline void Cb_free( Circular_buffer * const cb )
  { free( cb->buffer ); cb->buffer = 0; }

static inline void Cb_reset( Circular_buffer * const cb )
  { cb->get = 0; cb->put = 0; }

static inline unsigned Cb_empty( const Circular_buffer * const cb )
  { return cb->get == cb->put; }

static inline unsigned Cb_used_bytes( const Circular_buffer * const cb )
  { return ( (cb->get <= cb->put) ? 0 : cb->buffer_size ) + cb->put - cb->get; }

static inline unsigned Cb_free_bytes( const Circular_buffer * const cb )
  { return ( (cb->get <= cb->put) ? cb->buffer_size : 0 ) - cb->put + cb->get - 1; }

static inline uint8_t Cb_get_byte( Circular_buffer * const cb )
  {
  const uint8_t b = cb->buffer[cb->get];
  if( ++cb->get >= cb->buffer_size ) cb->get = 0;
  return b;
  }

static inline void Cb_put_byte( Circular_buffer * const cb, const uint8_t b )
  {
  cb->buffer[cb->put] = b;
  if( ++cb->put >= cb->buffer_size ) cb->put = 0;
  }


static bool Cb_unread_data( Circular_buffer * const cb, const unsigned size )
  {
  if( size > Cb_free_bytes( cb ) ) return false;
  if( cb->get >= size ) cb->get -= size;
  else cb->get = cb->buffer_size - size + cb->get;
  return true;
  }


/* Copy up to 'out_size' bytes to 'out_buffer' and update 'get'.
   If 'out_buffer' is null, the bytes are discarded.
   Return the number of bytes copied or discarded.
*/
static unsigned Cb_read_data( Circular_buffer * const cb,
                              uint8_t * const out_buffer,
                              const unsigned out_size )
  {
  unsigned size = 0;
  if( out_size == 0 ) return 0;
  if( cb->get > cb->put )
    {
    size = min( cb->buffer_size - cb->get, out_size );
    if( size > 0 )
      {
      if( out_buffer ) memcpy( out_buffer, cb->buffer + cb->get, size );
      cb->get += size;
      if( cb->get >= cb->buffer_size ) cb->get = 0;
      }
    }
  if( cb->get < cb->put )
    {
    const unsigned size2 = min( cb->put - cb->get, out_size - size );
    if( size2 > 0 )
      {
      if( out_buffer ) memcpy( out_buffer + size, cb->buffer + cb->get, size2 );
      cb->get += size2;
      size += size2;
      }
    }
  return size;
  }


/* Copy up to 'in_size' bytes from 'in_buffer' and update 'put'.
   Return the number of bytes copied.
*/
static unsigned Cb_write_data( Circular_buffer * const cb,
                               const uint8_t * const in_buffer,
                               const unsigned in_size )
  {
  unsigned size = 0;
  if( in_size == 0 ) return 0;
  if( cb->put >= cb->get )
    {
    size = min( cb->buffer_size - cb->put - (cb->get == 0), in_size );
    if( size > 0 )
      {
      memcpy( cb->buffer + cb->put, in_buffer, size );
      cb->put += size;
      if( cb->put >= cb->buffer_size ) cb->put = 0;
      }
    }
  if( cb->put < cb->get )
    {
    const unsigned size2 = min( cb->get - cb->put - 1, in_size - size );
    if( size2 > 0 )
      {
      memcpy( cb->buffer + cb->put, in_buffer + size, size2 );
      cb->put += size2;
      size += size2;
      }
    }
  return size;
  }