checksum_impl.h File Reference

#include "storage/bufpage.h"

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Data Structures
union	PGChecksummablePage

Macros
#define	N_SUMS   32
#define	FNV_PRIME   16777619
#define	CHECKSUM_COMP(checksum, value)

Functions
static uint32	pg_checksum_block (const PGChecksummablePage *page)
uint16	pg_checksum_page (char *page, BlockNumber blkno)

Variables
static const uint32	checksumBaseOffsets [N_SUMS]

Macro Definition Documentation

CHECKSUM_COMP

#define CHECKSUM_COMP	(		checksum,
			value
	)

Value:

do { \
    uint32 __tmp = (checksum) ^ (value); \
    (checksum) = __tmp * FNV_PRIME ^ (__tmp >> 17); \
} while (0)

Definition at line 135 of file checksum_impl.h.

FNV_PRIME

#define FNV_PRIME   16777619

Definition at line 108 of file checksum_impl.h.

N_SUMS

#define N_SUMS   32

Definition at line 106 of file checksum_impl.h.

Function Documentation

pg_checksum_block()

static uint32 pg_checksum_block ( const PGChecksummablePage *  page )

static

Definition at line 146 of file checksum_impl.h.

{
    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;
}

References Assert(), CHECKSUM_COMP, checksumBaseOffsets, PGChecksummablePage::data, i, j, and N_SUMS.

Referenced by pg_checksum_page().

pg_checksum_page()

uint16 pg_checksum_page	(	char *	page,
		BlockNumber	blkno
	)

Definition at line 187 of file checksum_impl.h.

{
    PGChecksummablePage *cpage = (PGChecksummablePage *) page;
    uint16      save_checksum;
    uint32      checksum;
 
    /* We only calculate the checksum for properly-initialized pages */
    Assert(!PageIsNew((Page) page));
 
    /*
     * Save pd_checksum and temporarily set it to zero, so that the checksum
     * calculation isn't affected by the old checksum stored on the page.
     * Restore it after, because actually updating the checksum is NOT part of
     * the API of this function.
     */
    save_checksum = cpage->phdr.pd_checksum;
    cpage->phdr.pd_checksum = 0;
    checksum = pg_checksum_block(cpage);
    cpage->phdr.pd_checksum = save_checksum;
 
    /* Mix in the block number to detect transposed pages */
    checksum ^= blkno;
 
    /*
     * Reduce to a uint16 (to fit in the pd_checksum field) with an offset of
     * one. That avoids checksums of zero, which seems like a good idea.
     */
    return (uint16) ((checksum % 65535) + 1);
}

References Assert(), PageIsNew(), PageHeaderData::pd_checksum, pg_checksum_block(), and PGChecksummablePage::phdr.

Referenced by modify_rel_block(), page_checksum_internal(), PageIsVerified(), PageSetChecksumCopy(), PageSetChecksumInplace(), rewriteVisibilityMap(), scan_file(), and verify_page_checksum().

Variable Documentation

checksumBaseOffsets

const uint32 checksumBaseOffsets[N_SUMS]

static

Initial value:

= {
    0x5B1F36E9, 0xB8525960, 0x02AB50AA, 0x1DE66D2A,
    0x79FF467A, 0x9BB9F8A3, 0x217E7CD2, 0x83E13D2C,
    0xF8D4474F, 0xE39EB970, 0x42C6AE16, 0x993216FA,
    0x7B093B5D, 0x98DAFF3C, 0xF718902A, 0x0B1C9CDB,
    0xE58F764B, 0x187636BC, 0x5D7B3BB1, 0xE73DE7DE,
    0x92BEC979, 0xCCA6C0B2, 0x304A0979, 0x85AA43D4,
    0x783125BB, 0x6CA8EAA2, 0xE407EAC6, 0x4B5CFC3E,
    0x9FBF8C76, 0x15CA20BE, 0xF2CA9FD3, 0x959BD756
}

Definition at line 121 of file checksum_impl.h.

Referenced by pg_checksum_block().