checksum_block.inc.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * checksum_block.inc.c
 *    Core algorithm for page checksums, semi-private to checksum_impl.h
 *    and checksum.c.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/checksum_block.inc.c
 *
 *-------------------------------------------------------------------------
 */
 
/* there is deliberately not an #ifndef CHECKSUM_BLOCK_INC_C here */
 
uint32      sums[N_SUMS];
uint32      result = 0;
uint32      i,
            j;
 
/* ensure that the size is compatible with the algorithm */
Assert(sizeof(PGChecksummablePage) == BLCKSZ);
 
/* initialize partial checksums to their corresponding offsets */
memcpy(sums, checksumBaseOffsets, sizeof(checksumBaseOffsets));
 
/* main checksum calculation */
for (i = 0; i < (uint32) (BLCKSZ / (sizeof(uint32) * N_SUMS)); i++)
    for (j = 0; j < N_SUMS; j++)
        CHECKSUM_COMP(sums[j], page->data[i][j]);
 
/* finally add in two rounds of zeroes for additional mixing */
for (i = 0; i < 2; i++)
    for (j = 0; j < N_SUMS; j++)
        CHECKSUM_COMP(sums[j], 0);
 
/* xor fold partial checksums together */
for (i = 0; i < N_SUMS; i++)
    result ^= sums[i];
 
return result;