/* * bzip2 is written by Julian Seward . * Adapted for busybox by Denys Vlasenko . * See README and LICENSE files in this directory for more information. */ /*-------------------------------------------------------------*/ /*--- Block sorting machinery ---*/ /*--- blocksort.c ---*/ /*-------------------------------------------------------------*/ /* ------------------------------------------------------------------ This file is part of bzip2/libbzip2, a program and library for lossless, block-sorting data compression. bzip2/libbzip2 version 1.0.4 of 20 December 2006 Copyright (C) 1996-2006 Julian Seward Please read the WARNING, DISCLAIMER and PATENTS sections in the README file. This program is released under the terms of the license contained in the file LICENSE. ------------------------------------------------------------------ */ /* #include "bzlib_private.h" */ #define mswap(zz1, zz2) \ { \ int32_t zztmp = zz1; \ zz1 = zz2; \ zz2 = zztmp; \ } static /* No measurable speed gain with inlining */ /* ALWAYS_INLINE */ void mvswap(uint32_t* ptr, int32_t zzp1, int32_t zzp2, int32_t zzn) { while (zzn > 0) { mswap(ptr[zzp1], ptr[zzp2]); zzp1++; zzp2++; zzn--; } } static ALWAYS_INLINE int32_t mmin(int32_t a, int32_t b) { return (a < b) ? a : b; } /*---------------------------------------------*/ /*--- Fallback O(N log(N)^2) sorting ---*/ /*--- algorithm, for repetitive blocks ---*/ /*---------------------------------------------*/ /*---------------------------------------------*/ static inline void fallbackSimpleSort(uint32_t* fmap, uint32_t* eclass, int32_t lo, int32_t hi) { int32_t i, j, tmp; uint32_t ec_tmp; if (lo == hi) return; if (hi - lo > 3) { for (i = hi-4; i >= lo; i--) { tmp = fmap[i]; ec_tmp = eclass[tmp]; for (j = i+4; j <= hi && ec_tmp > eclass[fmap[j]]; j += 4) fmap[j-4] = fmap[j]; fmap[j-4] = tmp; } } for (i = hi-1; i >= lo; i--) { tmp = fmap[i]; ec_tmp = eclass[tmp]; for (j = i+1; j <= hi && ec_tmp > eclass[fmap[j]]; j++) fmap[j-1] = fmap[j]; fmap[j-1] = tmp; } } /*---------------------------------------------*/ #define fpush(lz,hz) { \ stackLo[sp] = lz; \ stackHi[sp] = hz; \ sp++; \ } #define fpop(lz,hz) { \ sp--; \ lz = stackLo[sp]; \ hz = stackHi[sp]; \ } #define FALLBACK_QSORT_SMALL_THRESH 10 #define FALLBACK_QSORT_STACK_SIZE 100 static void fallbackQSort3(uint32_t* fmap, uint32_t* eclass, int32_t loSt, int32_t hiSt) { int32_t unLo, unHi, ltLo, gtHi, n, m; int32_t sp, lo, hi; uint32_t med, r, r3; int32_t stackLo[FALLBACK_QSORT_STACK_SIZE]; int32_t stackHi[FALLBACK_QSORT_STACK_SIZE]; r = 0; sp = 0; fpush(loSt, hiSt); while (sp > 0) { AssertH(sp < FALLBACK_QSORT_STACK_SIZE - 1, 1004); fpop(lo, hi); if (hi - lo < FALLBACK_QSORT_SMALL_THRESH) { fallbackSimpleSort(fmap, eclass, lo, hi); continue; } /* Random partitioning. Median of 3 sometimes fails to * avoid bad cases. Median of 9 seems to help but * looks rather expensive. This too seems to work but * is cheaper. Guidance for the magic constants * 7621 and 32768 is taken from Sedgewick's algorithms * book, chapter 35. */ r = ((r * 7621) + 1) % 32768; r3 = r % 3; if (r3 == 0) med = eclass[fmap[lo]]; else if (r3 == 1) med = eclass[fmap[(lo+hi)>>1]]; else med = eclass[fmap[hi]]; unLo = ltLo = lo; unHi = gtHi = hi; while (1) { while (1) { if (unLo > unHi) break; n = (int32_t)eclass[fmap[unLo]] - (int32_t)med; if (n == 0) { mswap(fmap[unLo], fmap[ltLo]); ltLo++; unLo++; continue; }; if (n > 0) break; unLo++; } while (1) { if (unLo > unHi) break; n = (int32_t)eclass[fmap[unHi]] - (int32_t)med; if (n == 0) { mswap(fmap[unHi], fmap[gtHi]); gtHi--; unHi--; continue; }; if (n < 0) break; unHi--; } if (unLo > unHi) break; mswap(fmap[unLo], fmap[unHi]); unLo++; unHi--; } AssertD(unHi == unLo-1, "fallbackQSort3(2)"); if (gtHi < ltLo) continue; n = mmin(ltLo-lo, unLo-ltLo); mvswap(fmap, lo, unLo-n, n); m = mmin(hi-gtHi, gtHi-unHi); mvswap(fmap, unLo, hi-m+1, m); n = lo + unLo - ltLo - 1; m = hi - (gtHi - unHi) + 1; if (n - lo > hi - m) { fpush(lo, n); fpush(m, hi); } else { fpush(m, hi); fpush(lo, n); } } } #undef fpush #undef fpop #undef FALLBACK_QSORT_SMALL_THRESH #undef FALLBACK_QSORT_STACK_SIZE /*---------------------------------------------*/ /* Pre: * nblock > 0 * eclass exists for [0 .. nblock-1] * ((uint8_t*)eclass) [0 .. nblock-1] holds block * ptr exists for [0 .. nblock-1] * * Post: * ((uint8_t*)eclass) [0 .. nblock-1] holds block * All other areas of eclass destroyed * fmap [0 .. nblock-1] holds sorted order * bhtab[0 .. 2+(nblock/32)] destroyed */ #define SET_BH(zz) bhtab[(zz) >> 5] |= (1 << ((zz) & 31)) #define CLEAR_BH(zz) bhtab[(zz) >> 5] &= ~(1 << ((zz) & 31)) #define ISSET_BH(zz) (bhtab[(zz) >> 5] & (1 << ((zz) & 31))) #define WORD_BH(zz) bhtab[(zz) >> 5] #define UNALIGNED_BH(zz) ((zz) & 0x01f) static void fallbackSort(uint32_t* fmap, uint32_t* eclass, uint32_t* bhtab, int32_t nblock) { int32_t ftab[257]; int32_t ftabCopy[256]; int32_t H, i, j, k, l, r, cc, cc1; int32_t nNotDone; int32_t nBhtab; uint8_t* eclass8 = (uint8_t*)eclass; /* * Initial 1-char radix sort to generate * initial fmap and initial BH bits. */ for (i = 0; i < 257; i++) ftab[i] = 0; for (i = 0; i < nblock; i++) ftab[eclass8[i]]++; for (i = 0; i < 256; i++) ftabCopy[i] = ftab[i]; j = ftab[0]; /* bbox: optimized */ for (i = 1; i < 257; i++) { j += ftab[i]; ftab[i] = j; } for (i = 0; i < nblock; i++) { j = eclass8[i]; k = ftab[j] - 1; ftab[j] = k; fmap[k] = i; } nBhtab = 2 + ((uint32_t)nblock / 32); /* bbox: unsigned div is easier */ for (i = 0; i < nBhtab; i++) bhtab[i] = 0; for (i = 0; i < 256; i++) SET_BH(ftab[i]); /* * Inductively refine the buckets. Kind-of an * "exponential radix sort" (!), inspired by the * Manber-Myers suffix array construction algorithm. */ /*-- set sentinel bits for block-end detection --*/ for (i = 0; i < 32; i++) { SET_BH(nblock + 2*i); CLEAR_BH(nblock + 2*i + 1); } /*-- the log(N) loop --*/ H = 1; while (1) { j = 0; for (i = 0; i < nblock; i++) { if (ISSET_BH(i)) j = i; k = fmap[i] - H; if (k < 0) k += nblock; eclass[k] = j; } nNotDone = 0; r = -1; while (1) { /*-- find the next non-singleton bucket --*/ k = r + 1; while (ISSET_BH(k) && UNALIGNED_BH(k)) k++; if (ISSET_BH(k)) { while (WORD_BH(k) == 0xffffffff) k += 32; while (ISSET_BH(k)) k++; } l = k - 1; if (l >= nblock) break; while (!ISSET_BH(k) && UNALIGNED_BH(k)) k++; if (!ISSET_BH(k)) { while (WORD_BH(k) == 0x00000000) k += 32; while (!ISSET_BH(k)) k++; } r = k - 1; if (r >= nblock) break; /*-- now [l, r] bracket current bucket --*/ if (r > l) { nNotDone += (r - l + 1); fallbackQSort3(fmap, eclass, l, r); /*-- scan bucket and generate header bits-- */ cc = -1; for (i = l; i <= r; i++) { cc1 = eclass[fmap[i]]; if (cc != cc1) { SET_BH(i); cc = cc1; }; } } } H *= 2; if (H > nblock || nNotDone == 0) break; } /* * Reconstruct the original block in * eclass8 [0 .. nblock-1], since the * previous phase destroyed it. */ j = 0; for (i = 0; i < nblock; i++) { while (ftabCopy[j] == 0) j++; ftabCopy[j]--; eclass8[fmap[i]] = (uint8_t)j; } AssertH(j < 256, 1005); } #undef SET_BH #undef CLEAR_BH #undef ISSET_BH #undef WORD_BH #undef UNALIGNED_BH /*---------------------------------------------*/ /*--- The main, O(N^2 log(N)) sorting ---*/ /*--- algorithm. Faster for "normal" ---*/ /*--- non-repetitive blocks. ---*/ /*---------------------------------------------*/ /*---------------------------------------------*/ static NOINLINE int mainGtU( uint32_t i1, uint32_t i2, uint8_t* block, uint16_t* quadrant, uint32_t nblock, int32_t* budget) { int32_t k; uint8_t c1, c2; uint16_t s1, s2; /* Loop unrolling here is actually very useful * (generated code is much simpler), * code size increase is only 270 bytes (i386) * but speeds up compression 10% overall */ #if CONFIG_BZIP2_FEATURE_SPEED >= 1 #define TIMES_8(code) \ code; code; code; code; \ code; code; code; code; #define TIMES_12(code) \ code; code; code; code; \ code; code; code; code; \ code; code; code; code; #else #define TIMES_8(code) \ { \ int nn = 8; \ do { \ code; \ } while (--nn); \ } #define TIMES_12(code) \ { \ int nn = 12; \ do { \ code; \ } while (--nn); \ } #endif AssertD(i1 != i2, "mainGtU"); TIMES_12( c1 = block[i1]; c2 = block[i2]; if (c1 != c2) return (c1 > c2); i1++; i2++; ) k = nblock + 8; do { TIMES_8( c1 = block[i1]; c2 = block[i2]; if (c1 != c2) return (c1 > c2); s1 = quadrant[i1]; s2 = quadrant[i2]; if (s1 != s2) return (s1 > s2); i1++; i2++; ) if (i1 >= nblock) i1 -= nblock; if (i2 >= nblock) i2 -= nblock; (*budget)--; k -= 8; } while (k >= 0); return False; } #undef TIMES_8 #undef TIMES_12 /*---------------------------------------------*/ /* * Knuth's increments seem to work better * than Incerpi-Sedgewick here. Possibly * because the number of elems to sort is * usually small, typically <= 20. */ static const int32_t incs[14] = { 1, 4, 13, 40, 121, 364, 1093, 3280, 9841, 29524, 88573, 265720, 797161, 2391484 }; static void mainSimpleSort(uint32_t* ptr, uint8_t* block, uint16_t* quadrant, int32_t nblock, int32_t lo, int32_t hi, int32_t d, int32_t* budget) { int32_t i, j, h, bigN, hp; uint32_t v; bigN = hi - lo + 1; if (bigN < 2) return; hp = 0; while (incs[hp] < bigN) hp++; hp--; for (; hp >= 0; hp--) { h = incs[hp]; i = lo + h; while (1) { /*-- copy 1 --*/ if (i > hi) break; v = ptr[i]; j = i; while (mainGtU(ptr[j-h]+d, v+d, block, quadrant, nblock, budget)) { ptr[j] = ptr[j-h]; j = j - h; if (j <= (lo + h - 1)) break; } ptr[j] = v; i++; /* 1.5% overall speedup, +290 bytes */ #if CONFIG_BZIP2_FEATURE_SPEED >= 3 /*-- copy 2 --*/ if (i > hi) break; v = ptr[i]; j = i; while (mainGtU(ptr[j-h]+d, v+d, block, quadrant, nblock, budget)) { ptr[j] = ptr[j-h]; j = j - h; if (j <= (lo + h - 1)) break; } ptr[j] = v; i++; /*-- copy 3 --*/ if (i > hi) break; v = ptr[i]; j = i; while (mainGtU(ptr[j-h]+d, v+d, block, quadrant, nblock, budget)) { ptr[j] = ptr[j-h]; j = j - h; if (j <= (lo + h - 1)) break; } ptr[j] = v; i++; #endif if (*budget < 0) return; } } } /*---------------------------------------------*/ /* * The following is an implementation of * an elegant 3-way quicksort for strings, * described in a paper "Fast Algorithms for * Sorting and Searching Strings", by Robert * Sedgewick and Jon L. Bentley. */ static ALWAYS_INLINE uint8_t mmed3(uint8_t a, uint8_t b, uint8_t c) { uint8_t t; if (a > b) { t = a; a = b; b = t; }; /* here b >= a */ if (b > c) { b = c; if (a > b) b = a; } return b; } #define mpush(lz,hz,dz) \ { \ stackLo[sp] = lz; \ stackHi[sp] = hz; \ stackD [sp] = dz; \ sp++; \ } #define mpop(lz,hz,dz) \ { \ sp--; \ lz = stackLo[sp]; \ hz = stackHi[sp]; \ dz = stackD [sp]; \ } #define mnextsize(az) (nextHi[az] - nextLo[az]) #define mnextswap(az,bz) \ { \ int32_t tz; \ tz = nextLo[az]; nextLo[az] = nextLo[bz]; nextLo[bz] = tz; \ tz = nextHi[az]; nextHi[az] = nextHi[bz]; nextHi[bz] = tz; \ tz = nextD [az]; nextD [az] = nextD [bz]; nextD [bz] = tz; \ } #define MAIN_QSORT_SMALL_THRESH 20 #define MAIN_QSORT_DEPTH_THRESH (BZ_N_RADIX + BZ_N_QSORT) #define MAIN_QSORT_STACK_SIZE 100 static NOINLINE void mainQSort3(uint32_t* ptr, uint8_t* block, uint16_t* quadrant, int32_t nblock, int32_t loSt, int32_t hiSt, int32_t dSt, int32_t* budget) { int32_t unLo, unHi, ltLo, gtHi, n, m, med; int32_t sp, lo, hi, d; int32_t stackLo[MAIN_QSORT_STACK_SIZE]; int32_t stackHi[MAIN_QSORT_STACK_SIZE]; int32_t stackD [MAIN_QSORT_STACK_SIZE]; int32_t nextLo[3]; int32_t nextHi[3]; int32_t nextD [3]; sp = 0; mpush(loSt, hiSt, dSt); while (sp > 0) { AssertH(sp < MAIN_QSORT_STACK_SIZE - 2, 1001); mpop(lo, hi, d); if (hi - lo < MAIN_QSORT_SMALL_THRESH || d > MAIN_QSORT_DEPTH_THRESH ) { mainSimpleSort(ptr, block, quadrant, nblock, lo, hi, d, budget); if (*budget < 0) return; continue; } med = (int32_t) mmed3(block[ptr[lo ] + d], block[ptr[hi ] + d], block[ptr[(lo+hi) >> 1] + d]); unLo = ltLo = lo; unHi = gtHi = hi; while (1) { while (1) { if (unLo > unHi) break; n = ((int32_t)block[ptr[unLo]+d]) - med; if (n == 0) { mswap(ptr[unLo], ptr[ltLo]); ltLo++; unLo++; continue; }; if (n > 0) break; unLo++; } while (1) { if (unLo > unHi) break; n = ((int32_t)block[ptr[unHi]+d]) - med; if (n == 0) { mswap(ptr[unHi], ptr[gtHi]); gtHi--; unHi--; continue; }; if (n < 0) break; unHi--; } if (unLo > unHi) break; mswap(ptr[unLo], ptr[unHi]); unLo++; unHi--; } AssertD(unHi == unLo-1, "mainQSort3(2)"); if (gtHi < ltLo) { mpush(lo, hi, d + 1); continue; } n = mmin(ltLo-lo, unLo-ltLo); mvswap(ptr, lo, unLo-n, n); m = mmin(hi-gtHi, gtHi-unHi); mvswap(ptr, unLo, hi-m+1, m); n = lo + unLo - ltLo - 1; m = hi - (gtHi - unHi) + 1; nextLo[0] = lo; nextHi[0] = n; nextD[0] = d; nextLo[1] = m; nextHi[1] = hi; nextD[1] = d; nextLo[2] = n+1; nextHi[2] = m-1; nextD[2] = d+1; if (mnextsize(0) < mnextsize(1)) mnextswap(0, 1); if (mnextsize(1) < mnextsize(2)) mnextswap(1, 2); if (mnextsize(0) < mnextsize(1)) mnextswap(0, 1); AssertD (mnextsize(0) >= mnextsize(1), "mainQSort3(8)"); AssertD (mnextsize(1) >= mnextsize(2), "mainQSort3(9)"); mpush(nextLo[0], nextHi[0], nextD[0]); mpush(nextLo[1], nextHi[1], nextD[1]); mpush(nextLo[2], nextHi[2], nextD[2]); } } #undef mpush #undef mpop #undef mnextsize #undef mnextswap #undef MAIN_QSORT_SMALL_THRESH #undef MAIN_QSORT_DEPTH_THRESH #undef MAIN_QSORT_STACK_SIZE /*---------------------------------------------*/ /* Pre: * nblock > N_OVERSHOOT * block32 exists for [0 .. nblock-1 +N_OVERSHOOT] * ((uint8_t*)block32) [0 .. nblock-1] holds block * ptr exists for [0 .. nblock-1] * * Post: * ((uint8_t*)block32) [0 .. nblock-1] holds block * All other areas of block32 destroyed * ftab[0 .. 65536] destroyed * ptr [0 .. nblock-1] holds sorted order * if (*budget < 0), sorting was abandoned */ #define BIGFREQ(b) (ftab[((b)+1) << 8] - ftab[(b) << 8]) #define SETMASK (1 << 21) #define CLEARMASK (~(SETMASK)) static NOINLINE void mainSort(EState* state, uint32_t* ptr, uint8_t* block, uint16_t* quadrant, uint32_t* ftab, int32_t nblock, int32_t* budget) { int32_t i, j, k, ss, sb; uint8_t c1; int32_t numQSorted; uint16_t s; Bool bigDone[256]; /* bbox: moved to EState to save stack int32_t runningOrder[256]; int32_t copyStart[256]; int32_t copyEnd [256]; */ #define runningOrder (state->mainSort__runningOrder) #define copyStart (state->mainSort__copyStart) #define copyEnd (state->mainSort__copyEnd) /*-- set up the 2-byte frequency table --*/ /* was: for (i = 65536; i >= 0; i--) ftab[i] = 0; */ memset(ftab, 0, 65537 * sizeof(ftab[0])); j = block[0] << 8; i = nblock - 1; /* 3%, +300 bytes */ #if CONFIG_BZIP2_FEATURE_SPEED >= 2 for (; i >= 3; i -= 4) { quadrant[i] = 0; j = (j >> 8) | (((uint16_t)block[i]) << 8); ftab[j]++; quadrant[i-1] = 0; j = (j >> 8) | (((uint16_t)block[i-1]) << 8); ftab[j]++; quadrant[i-2] = 0; j = (j >> 8) | (((uint16_t)block[i-2]) << 8); ftab[j]++; quadrant[i-3] = 0; j = (j >> 8) | (((uint16_t)block[i-3]) << 8); ftab[j]++; } #endif for (; i >= 0; i--) { quadrant[i] = 0; j = (j >> 8) | (((uint16_t)block[i]) << 8); ftab[j]++; } /*-- (emphasises close relationship of block & quadrant) --*/ for (i = 0; i < BZ_N_OVERSHOOT; i++) { block [nblock+i] = block[i]; quadrant[nblock+i] = 0; } /*-- Complete the initial radix sort --*/ j = ftab[0]; /* bbox: optimized */ for (i = 1; i <= 65536; i++) { j += ftab[i]; ftab[i] = j; } s = block[0] << 8; i = nblock - 1; #if CONFIG_BZIP2_FEATURE_SPEED >= 2 for (; i >= 3; i -= 4) { s = (s >> 8) | (block[i] << 8); j = ftab[s] - 1; ftab[s] = j; ptr[j] = i; s = (s >> 8) | (block[i-1] << 8); j = ftab[s] - 1; ftab[s] = j; ptr[j] = i-1; s = (s >> 8) | (block[i-2] << 8); j = ftab[s] - 1; ftab[s] = j; ptr[j] = i-2; s = (s >> 8) | (block[i-3] << 8); j = ftab[s] - 1; ftab[s] = j; ptr[j] = i-3; } #endif for (; i >= 0; i--) { s = (s >> 8) | (block[i] << 8); j = ftab[s] - 1; ftab[s] = j; ptr[j] = i; } /* * Now ftab contains the first loc of every small bucket. * Calculate the running order, from smallest to largest * big bucket. */ for (i = 0; i <= 255; i++) { bigDone [i] = False; runningOrder[i] = i; } { int32_t vv; /* bbox: was: int32_t h = 1; */ /* do h = 3 * h + 1; while (h <= 256); */ uint32_t h = 364; do { /*h = h / 3;*/ h = (h * 171) >> 9; /* bbox: fast h/3 */ for (i = h; i <= 255; i++) { vv = runningOrder[i]; j = i; while (BIGFREQ(runningOrder[j-h]) > BIGFREQ(vv)) { runningOrder[j] = runningOrder[j-h]; j = j - h; if (j <= (h - 1)) goto zero; } zero: runningOrder[j] = vv; } } while (h != 1); } /* * The main sorting loop. */ numQSorted = 0; for (i = 0; i <= 255; i++) { /* * Process big buckets, starting with the least full. * Basically this is a 3-step process in which we call * mainQSort3 to sort the small buckets [ss, j], but * also make a big effort to avoid the calls if we can. */ ss = runningOrder[i]; /* * Step 1: * Complete the big bucket [ss] by quicksorting * any unsorted small buckets [ss, j], for j != ss. * Hopefully previous pointer-scanning phases have already * completed many of the small buckets [ss, j], so * we don't have to sort them at all. */ for (j = 0; j <= 255; j++) { if (j != ss) { sb = (ss << 8) + j; if (!(ftab[sb] & SETMASK)) { int32_t lo = ftab[sb] & CLEARMASK; int32_t hi = (ftab[sb+1] & CLEARMASK) - 1; if (hi > lo) { mainQSort3( ptr, block, quadrant, nblock, lo, hi, BZ_N_RADIX, budget ); if (*budget < 0) return; numQSorted += (hi - lo + 1); } } ftab[sb] |= SETMASK; } } AssertH(!bigDone[ss], 1006); /* * Step 2: * Now scan this big bucket [ss] so as to synthesise the * sorted order for small buckets [t, ss] for all t, * including, magically, the bucket [ss,ss] too. * This will avoid doing Real Work in subsequent Step 1's. */ { for (j = 0; j <= 255; j++) { copyStart[j] = ftab[(j << 8) + ss] & CLEARMASK; copyEnd [j] = (ftab[(j << 8) + ss + 1] & CLEARMASK) - 1; } for (j = ftab[ss << 8] & CLEARMASK; j < copyStart[ss]; j++) { k = ptr[j] - 1; if (k < 0) k += nblock; c1 = block[k]; if (!bigDone[c1]) ptr[copyStart[c1]++] = k; } for (j = (ftab[(ss+1) << 8] & CLEARMASK) - 1; j > copyEnd[ss]; j--) { k = ptr[j]-1; if (k < 0) k += nblock; c1 = block[k]; if (!bigDone[c1]) ptr[copyEnd[c1]--] = k; } } /* Extremely rare case missing in bzip2-1.0.0 and 1.0.1. * Necessity for this case is demonstrated by compressing * a sequence of approximately 48.5 million of character * 251; 1.0.0/1.0.1 will then die here. */ AssertH((copyStart[ss]-1 == copyEnd[ss]) \ || (copyStart[ss] == 0 && copyEnd[ss] == nblock-1), 1007); for (j = 0; j <= 255; j++) ftab[(j << 8) + ss] |= SETMASK; /* * Step 3: * The [ss] big bucket is now done. Record this fact, * and update the quadrant descriptors. Remember to * update quadrants in the overshoot area too, if * necessary. The "if (i < 255)" test merely skips * this updating for the last bucket processed, since * updating for the last bucket is pointless. * * The quadrant array provides a way to incrementally * cache sort orderings, as they appear, so as to * make subsequent comparisons in fullGtU() complete * faster. For repetitive blocks this makes a big * difference (but not big enough to be able to avoid * the fallback sorting mechanism, exponential radix sort). * * The precise meaning is: at all times: * * for 0 <= i < nblock and 0 <= j <= nblock * * if block[i] != block[j], * * then the relative values of quadrant[i] and * quadrant[j] are meaningless. * * else { * if quadrant[i] < quadrant[j] * then the string starting at i lexicographically * precedes the string starting at j * * else if quadrant[i] > quadrant[j] * then the string starting at j lexicographically * precedes the string starting at i * * else * the relative ordering of the strings starting * at i and j has not yet been determined. * } */ bigDone[ss] = True; if (i < 255) { int32_t bbStart = ftab[ss << 8] & CLEARMASK; int32_t bbSize = (ftab[(ss+1) << 8] & CLEARMASK) - bbStart; int32_t shifts = 0; while ((bbSize >> shifts) > 65534) shifts++; for (j = bbSize-1; j >= 0; j--) { int32_t a2update = ptr[bbStart + j]; uint16_t qVal = (uint16_t)(j >> shifts); quadrant[a2update] = qVal; if (a2update < BZ_N_OVERSHOOT) quadrant[a2update + nblock] = qVal; } AssertH(((bbSize-1) >> shifts) <= 65535, 1002); } } #undef runningOrder #undef copyStart #undef copyEnd } #undef BIGFREQ #undef SETMASK #undef CLEARMASK /*---------------------------------------------*/ /* Pre: * nblock > 0 * arr2 exists for [0 .. nblock-1 +N_OVERSHOOT] * ((uint8_t*)arr2)[0 .. nblock-1] holds block * arr1 exists for [0 .. nblock-1] * * Post: * ((uint8_t*)arr2) [0 .. nblock-1] holds block * All other areas of block destroyed * ftab[0 .. 65536] destroyed * arr1[0 .. nblock-1] holds sorted order */ static NOINLINE void BZ2_blockSort(EState* s) { /* In original bzip2 1.0.4, it's a parameter, but 30 * (which was the default) should work ok. */ enum { wfact = 30 }; uint32_t* ptr = s->ptr; uint8_t* block = s->block; uint32_t* ftab = s->ftab; int32_t nblock = s->nblock; uint16_t* quadrant; int32_t budget; int32_t i; if (nblock < 10000) { fallbackSort(s->arr1, s->arr2, ftab, nblock); } else { /* Calculate the location for quadrant, remembering to get * the alignment right. Assumes that &(block[0]) is at least * 2-byte aligned -- this should be ok since block is really * the first section of arr2. */ i = nblock + BZ_N_OVERSHOOT; if (i & 1) i++; quadrant = (uint16_t*)(&(block[i])); /* (wfact-1) / 3 puts the default-factor-30 * transition point at very roughly the same place as * with v0.1 and v0.9.0. * Not that it particularly matters any more, since the * resulting compressed stream is now the same regardless * of whether or not we use the main sort or fallback sort. */ budget = nblock * ((wfact-1) / 3); mainSort(s, ptr, block, quadrant, ftab, nblock, &budget); if (budget < 0) { fallbackSort(s->arr1, s->arr2, ftab, nblock); } } s->origPtr = -1; for (i = 0; i < s->nblock; i++) if (ptr[i] == 0) { s->origPtr = i; break; }; AssertH(s->origPtr != -1, 1003); } /*-------------------------------------------------------------*/ /*--- end blocksort.c ---*/ /*-------------------------------------------------------------*/