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Use a power of generator representation of GF(256) multiplication group

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to save space time and complexity.

	* grub-core/disk/raid6_recover.c (raid6_table1): Removed.
	(raid6_table2): Likewise.
	(powx): New array.
	(powx_inv): Likewise.
	(poly): New const.
	(grub_raid_block_mul): Replace with ...
	(grub_raid_block_mulx): ...this.
	(grub_raid6_init_table): Rewritten.
	(grub_raid6_recover): Use power of generator representation.
This commit is contained in:
Vladimir 'phcoder' Serbinenko 2011-11-04 13:27:50 +01:00
parent 09e2763fb1
commit 11ee4389e2
2 changed files with 42 additions and 54 deletions
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15
ChangeLog
View file

@ -1,3 +1,18 @@
2011-11-04 Vladimir Serbinenko <phcoder@gmail.com>
Use a power of generator representation of GF(256) multiplication group
to save space time and complexity.
* grub-core/disk/raid6_recover.c (raid6_table1): Removed.
(raid6_table2): Likewise.
(powx): New array.
(powx_inv): Likewise.
(poly): New const.
(grub_raid_block_mul): Replace with ...
(grub_raid_block_mulx): ...this.
(grub_raid6_init_table): Rewritten.
(grub_raid6_recover): Use power of generator representation.
2011-11-04 Vladimir Serbinenko <phcoder@gmail.com> 2011-11-04 Vladimir Serbinenko <phcoder@gmail.com>
* grub-core/disk/raid6_recover.c (grub_raid6_recover): Get start_sector * grub-core/disk/raid6_recover.c (grub_raid6_recover): Get start_sector

77
grub-core/disk/raid6_recover.c
View file

@ -26,66 +26,39 @@
GRUB_MOD_LICENSE ("GPLv3+"); GRUB_MOD_LICENSE ("GPLv3+");
static grub_uint8_t raid6_table1[256][256]; /* x**y. */
static grub_uint8_t raid6_table2[256][256]; static grub_uint8_t powx[255 * 2];
/* Such an s that x**s = y */
static int powx_inv[256];
static const grub_uint8_t poly = 0x1d;
static void static void
grub_raid_block_mul (grub_uint8_t mul, char *buf, int size) grub_raid_block_mulx (int mul, char *buf, int size)
{ {
int i; int i;
grub_uint8_t *p; grub_uint8_t *p;
p = (grub_uint8_t *) buf; p = (grub_uint8_t *) buf;
for (i = 0; i < size; i++, p++) for (i = 0; i < size; i++, p++)
*p = raid6_table1[mul][*p]; if (*p)
*p = powx[mul + powx_inv[*p]];
} }
static void static void
grub_raid6_init_table (void) grub_raid6_init_table (void)
{ {
int i, j; int i;
for (i = 0; i < 256; i++) grub_uint8_t cur = 1;
raid6_table1[i][1] = raid6_table1[1][i] = i; for (i = 0; i < 255; i++)
for (i = 2; i < 256; i++)
for (j = i; j < 256; j++)
{ {
int n; powx[i] = cur;
grub_uint8_t c; powx[i + 255] = cur;
powx_inv[cur] = i;
n = i >> 1; if (cur & 0x80)
cur = (cur << 1) ^ poly;
c = raid6_table1[n][j]; else
c = (c << 1) ^ ((c & 0x80) ? 0x1d : 0); cur <<= 1;
if (i & 1)
c ^= j;
raid6_table1[j][i] = raid6_table1[i][j] = c;
}
raid6_table2[0][0] = 1;
for (i = 1; i < 256; i++)
raid6_table2[i][i] = raid6_table1[raid6_table2[i - 1][i - 1]][2];
for (i = 0; i < 254; i++)
for (j = 0; j < 254; j++)
{
grub_uint8_t c, n;
int k;
if (i == j)
continue;
k = i - j;
if (k < 0)
k += 255;
c = n = raid6_table2[k][k] ^ 1;
for (k = 0; k < 253; k++)
c = raid6_table1[c][n];
raid6_table2[i][j] = raid6_table1[raid6_table2[255 - j][255 - j]][c];
} }
} }
@ -126,7 +99,7 @@ grub_raid6_recover (struct grub_raid_array *array, int disknr, int p,
0, size, buf))) 0, size, buf)))
{ {
grub_raid_block_xor (pbuf, buf, size); grub_raid_block_xor (pbuf, buf, size);
grub_raid_block_mul (raid6_table2[i][i], buf, size); grub_raid_block_mulx (i, buf, size);
grub_raid_block_xor (qbuf, buf, size); grub_raid_block_xor (qbuf, buf, size);
} }
else else
@ -173,13 +146,13 @@ grub_raid6_recover (struct grub_raid_array *array, int disknr, int p,
goto quit; goto quit;
grub_raid_block_xor (buf, qbuf, size); grub_raid_block_xor (buf, qbuf, size);
grub_raid_block_mul (raid6_table2[255 - bad1][255 - bad1], buf, grub_raid_block_mulx (255 - bad1, buf,
size); size);
} }
else else
{ {
/* Two bad devices */ /* Two bad devices */
grub_uint8_t c; int c;
if ((! array->members[p].device) || (! array->members[q].device)) if ((! array->members[p].device) || (! array->members[q].device))
{ {
@ -201,11 +174,11 @@ grub_raid6_recover (struct grub_raid_array *array, int disknr, int p,
grub_raid_block_xor (qbuf, buf, size); grub_raid_block_xor (qbuf, buf, size);
c = raid6_table2[bad2][bad1]; c = (255 - bad1 + (255 - powx_inv[(powx[bad2 - bad1 + 255] ^ 1)])) % 255;
grub_raid_block_mul (c, qbuf, size); grub_raid_block_mulx (c, qbuf, size);
c = raid6_table1[raid6_table2[bad2][bad2]][c]; c = (bad2 + c) % 255;
grub_raid_block_mul (c, pbuf, size); grub_raid_block_mulx (c, pbuf, size);
grub_raid_block_xor (pbuf, qbuf, size); grub_raid_block_xor (pbuf, qbuf, size);
grub_memcpy (buf, pbuf, size); grub_memcpy (buf, pbuf, size);