gistfile1.c

/* old, one loop
 * 
 * With not enough data (< 4096):
 *   mem_read (..., 1, 4096): 162.099252s (100000000 runs)
 *   mem_read (..., 4096, 1): 0.967107s (100000000 runs)
 * With enough data (>= 4096):
 *   mem_read (..., 1, 4096): 2274.210934 (100000000 runs)
 *   mem_read (..., 4096, 1): 10.416469 (100000000 runs)
 */

static size_t
mem_read (MIO *mio,
          void *ptr,
          size_t size,
          size_t nmemb)
{
  size_t n_read = 0;
  
  if (size != 0 && nmemb != 0) {
    if (mio->impl.mem.ungetch != EOF) {
      *((unsigned char *) ptr) = (unsigned char) mio->impl.mem.ungetch;
      mio->impl.mem.ungetch = EOF;
      mio->impl.mem.pos++;
      if (size == 1) {
        n_read++;
      } else if (mio->impl.mem.pos + (size - 1) <= mio->impl.mem.size) {
        memcpy (&(((unsigned char *) ptr)[1]),
                &mio->impl.mem.buf[mio->impl.mem.pos], size - 1);
        mio->impl.mem.pos += size - 1;
        n_read++;
      }
    }
    for (; n_read < nmemb; n_read++) {
      if (mio->impl.mem.pos + size > mio->impl.mem.size) {
        break;
      } else {
        memcpy (&(((unsigned char *) ptr)[n_read * size]),
                &mio->impl.mem.buf[mio->impl.mem.pos], size);
        mio->impl.mem.pos += size;
      }
    }
    if (mio->impl.mem.pos >= mio->impl.mem.size) {
      mio->impl.mem.eof = TRUE;
    }
  }
  
  return n_read;
}

/* new, no loops
 * 
 * 
 * With not enough data (< 4096):
 *   mem_read (..., 1, 4096): 2.753983s (100000000 runs)
 *   mem_read (..., 4096, 1): 1.605477s (100000000 runs)
 * With enough data (>= 4096):
 *   mem_read (..., 1, 4096): 11.102533 (100000000 runs)
 *   mem_read (..., 4096, 1): 11.146004 (100000000 runs)
 */

static size_t
mem_read (MIO *mio,
          void *ptr_,
          size_t size,
          size_t nmemb)
{
  size_t n_read = 0;
  
  if (size != 0 /*&& nmemb != 0*/) {
    size_t block_avail = (mio->impl.mem.size - mio->impl.mem.pos) / size;
    size_t copy_blocks = MIN (block_avail, nmemb);
    unsigned char *ptr = ptr_;
    
    if (copy_blocks > 0) {
      if (mio->impl.mem.ungetch != EOF) {
        *ptr = (unsigned char) mio->impl.mem.ungetch;
        mio->impl.mem.ungetch = EOF;
        if (size > 1) {
          memcpy (ptr + 1, &mio->impl.mem.buf[mio->impl.mem.pos + 1], size - 1);
        }
        mio->impl.mem.pos += size;
        ptr += size;
        n_read++;
        copy_blocks--;
      }
      
      /*if (copy_blocks > 0)*/ {
        size_t copy_size = size * copy_blocks;
        memcpy (ptr, &mio->impl.mem.buf[mio->impl.mem.pos], copy_size);
        mio->impl.mem.pos += copy_size;
        n_read += copy_blocks;
      }
    }
    if (mio->impl.mem.pos >= mio->impl.mem.size) {
      mio->impl.mem.eof = TRUE;
    }
  }
  
  return n_read;
}