lib/crc/s390/crc32be-vx.c

Source file repositories/reference/linux-study-clean/lib/crc/s390/crc32be-vx.c

File Facts

System
Linux kernel
Corpus path
lib/crc/s390/crc32be-vx.c
Extension
.c
Size
5544 bytes
Lines
175
Domain
Kernel Services
Bucket
lib
Inferred role
Kernel Services: implementation source
Status
source implementation candidate

Why This File Exists

Shared kernel service surface used by multiple subsystems, including helpers, cryptography, virtualization support, and async I/O infrastructure.

Dependency Surface

Detected Declarations

Annotated Snippet

#include <linux/types.h>
#include <asm/fpu.h>
#include "crc32-vx.h"

/* Vector register range containing CRC-32 constants */
#define CONST_R1R2		9
#define CONST_R3R4		10
#define CONST_R5		11
#define CONST_R6		12
#define CONST_RU_POLY		13
#define CONST_CRC_POLY		14

/*
 * The CRC-32 constant block contains reduction constants to fold and
 * process particular chunks of the input data stream in parallel.
 *
 * For the CRC-32 variants, the constants are precomputed according to
 * these definitions:
 *
 *	R1 = x4*128+64 mod P(x)
 *	R2 = x4*128    mod P(x)
 *	R3 = x128+64   mod P(x)
 *	R4 = x128      mod P(x)
 *	R5 = x96       mod P(x)
 *	R6 = x64       mod P(x)
 *
 *	Barret reduction constant, u, is defined as floor(x**64 / P(x)).
 *
 *	where P(x) is the polynomial in the normal domain and the P'(x) is the
 *	polynomial in the reversed (bitreflected) domain.
 *
 * Note that the constant definitions below are extended in order to compute
 * intermediate results with a single VECTOR GALOIS FIELD MULTIPLY instruction.
 * The rightmost doubleword can be 0 to prevent contribution to the result or
 * can be multiplied by 1 to perform an XOR without the need for a separate
 * VECTOR EXCLUSIVE OR instruction.
 *
 * CRC-32 (IEEE 802.3 Ethernet, ...) polynomials:
 *
 *	P(x)  = 0x04C11DB7
 *	P'(x) = 0xEDB88320
 */

static unsigned long constants_CRC_32_BE[] = {
	0x08833794c, 0x0e6228b11,	/* R1, R2 */
	0x0c5b9cd4c, 0x0e8a45605,	/* R3, R4 */
	0x0f200aa66, 1UL << 32,		/* R5, x32 */
	0x0490d678d, 1,			/* R6, 1 */
	0x104d101df, 0,			/* u */
	0x104C11DB7, 0,			/* P(x) */
};

/**
 * crc32_be_vgfm_16 - Compute CRC-32 (BE variant) with vector registers
 * @crc: Initial CRC value, typically ~0.
 * @buf: Input buffer pointer, performance might be improved if the
 *	  buffer is on a doubleword boundary.
 * @size: Size of the buffer, must be 64 bytes or greater.
 *
 * Register usage:
 *	V0:	Initial CRC value and intermediate constants and results.
 *	V1..V4:	Data for CRC computation.
 *	V5..V8:	Next data chunks that are fetched from the input buffer.
 *	V9..V14: CRC-32 constants.
 */
u32 crc32_be_vgfm_16(u32 crc, unsigned char const *buf, size_t size)
{
	/* Load CRC-32 constants */
	fpu_vlm(CONST_R1R2, CONST_CRC_POLY, &constants_CRC_32_BE);
	fpu_vzero(0);

	/* Load the initial CRC value into the leftmost word of V0. */
	fpu_vlvgf(0, crc, 0);

	/* Load a 64-byte data chunk and XOR with CRC */
	fpu_vlm(1, 4, buf);
	fpu_vx(1, 0, 1);
	buf += 64;
	size -= 64;

	while (size >= 64) {
		/* Load the next 64-byte data chunk into V5 to V8 */
		fpu_vlm(5, 8, buf);

		/*
		 * Perform a GF(2) multiplication of the doublewords in V1 with
		 * the reduction constants in V0.  The intermediate result is
		 * then folded (accumulated) with the next data chunk in V5 and
		 * stored in V1.  Repeat this step for the register contents
		 * in V2, V3, and V4 respectively.

Annotation

Implementation Notes