From 11ee4389e27c9e776d598bc90f452cd3918982ff Mon Sep 17 00:00:00 2001 From: Vladimir 'phcoder' Serbinenko Date: Fri, 4 Nov 2011 13:27:50 +0100 Subject: [PATCH] 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. --- ChangeLog | 15 +++++++ grub-core/disk/raid6_recover.c | 81 ++++++++++++---------------------- 2 files changed, 42 insertions(+), 54 deletions(-) diff --git a/ChangeLog b/ChangeLog index f8813f259..b9e32f0e0 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,18 @@ +2011-11-04 Vladimir Serbinenko + + 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 * grub-core/disk/raid6_recover.c (grub_raid6_recover): Get start_sector diff --git a/grub-core/disk/raid6_recover.c b/grub-core/disk/raid6_recover.c index 54dc612ee..e91992547 100644 --- a/grub-core/disk/raid6_recover.c +++ b/grub-core/disk/raid6_recover.c @@ -26,67 +26,40 @@ GRUB_MOD_LICENSE ("GPLv3+"); -static grub_uint8_t raid6_table1[256][256]; -static grub_uint8_t raid6_table2[256][256]; +/* x**y. */ +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 -grub_raid_block_mul (grub_uint8_t mul, char *buf, int size) +grub_raid_block_mulx (int mul, char *buf, int size) { int i; grub_uint8_t *p; p = (grub_uint8_t *) buf; for (i = 0; i < size; i++, p++) - *p = raid6_table1[mul][*p]; + if (*p) + *p = powx[mul + powx_inv[*p]]; } static void grub_raid6_init_table (void) { - int i, j; + int i; - for (i = 0; i < 256; i++) - raid6_table1[i][1] = raid6_table1[1][i] = i; - - for (i = 2; i < 256; i++) - for (j = i; j < 256; j++) - { - int n; - grub_uint8_t c; - - n = i >> 1; - - c = raid6_table1[n][j]; - c = (c << 1) ^ ((c & 0x80) ? 0x1d : 0); - 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]; - } + grub_uint8_t cur = 1; + for (i = 0; i < 255; i++) + { + powx[i] = cur; + powx[i + 255] = cur; + powx_inv[cur] = i; + if (cur & 0x80) + cur = (cur << 1) ^ poly; + else + cur <<= 1; + } } static grub_err_t @@ -126,7 +99,7 @@ grub_raid6_recover (struct grub_raid_array *array, int disknr, int p, 0, size, buf))) { 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); } else @@ -173,13 +146,13 @@ grub_raid6_recover (struct grub_raid_array *array, int disknr, int p, goto quit; 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); } else { /* Two bad devices */ - grub_uint8_t c; + int c; 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); - c = raid6_table2[bad2][bad1]; - grub_raid_block_mul (c, qbuf, size); + c = (255 - bad1 + (255 - powx_inv[(powx[bad2 - bad1 + 255] ^ 1)])) % 255; + grub_raid_block_mulx (c, qbuf, size); - c = raid6_table1[raid6_table2[bad2][bad2]][c]; - grub_raid_block_mul (c, pbuf, size); + c = (bad2 + c) % 255; + grub_raid_block_mulx (c, pbuf, size); grub_raid_block_xor (pbuf, qbuf, size); grub_memcpy (buf, pbuf, size);