The Tor Browser: security/nss/lib/freebl/mpi/utils/sieve.c@6474c204b198 (annotated)

security/nss/lib/freebl/mpi/utils/sieve.c@6474c204b198 (annotated)

security/nss/lib/freebl/mpi/utils/sieve.c

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /*
  * sieve.c
  *
  * Finds prime numbers using the Sieve of Eratosthenes
  *
  * This implementation uses a bitmap to represent all odd integers in a
  * given range.  We iterate over this bitmap, crossing off the
  * multiples of each prime we find.  At the end, all the remaining set
  * bits correspond to prime integers.
  *
  * Here, we make two passes -- once we have generated a sieve-ful of
  * primes, we copy them out, reset the sieve using the highest
  * generated prime from the first pass as a base.  Then we cross out
  * all the multiples of all the primes we found the first time through,
  * and re-sieve.  In this way, we get double use of the memory we
  * allocated for the sieve the first time though.  Since we also
  * implicitly ignore multiples of 2, this amounts to 4 times the
  * values.
  *
  * This could (and probably will) be generalized to re-use the sieve a
  * few more times.
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include <stdio.h>
 #include <stdlib.h>
 #include <limits.h>
 typedef unsigned char  byte;
 typedef struct {
   int   size;
   byte *bits;
   long  base;
   int   next;
   int   nbits;
 } sieve;
 void sieve_init(sieve *sp, long base, int nbits);
 void sieve_grow(sieve *sp, int nbits);
 long sieve_next(sieve *sp);
 void sieve_reset(sieve *sp, long base);
 void sieve_cross(sieve *sp, long val);
 void sieve_clear(sieve *sp);
 #define S_ISSET(S, B)  (((S)->bits[(B)/CHAR_BIT]>>((B)%CHAR_BIT))&1)
 #define S_SET(S, B)    ((S)->bits[(B)/CHAR_BIT]|=(1<<((B)%CHAR_BIT)))
 #define S_CLR(S, B)    ((S)->bits[(B)/CHAR_BIT]&=~(1<<((B)%CHAR_BIT)))
 #define S_VAL(S, B)    ((S)->base+(2*(B)))
 #define S_BIT(S, V)    (((V)-((S)->base))/2)
 int main(int argc, char *argv[])
 {
   sieve   s;
   long    pr, *p;
   int     c, ix, cur = 0;
   if(argc < 2) {
     fprintf(stderr, "Usage: %s <width>\n", argv[0]);
     return 1;
   }
   c = atoi(argv[1]);
   if(c < 0) c = -c;
   fprintf(stderr, "%s: sieving to %d positions\n", argv[0], c);
   sieve_init(&s, 3, c);
   c = 0;
   while((pr = sieve_next(&s)) > 0) {
     ++c;
   }
   p = calloc(c, sizeof(long));
   if(!p) {
     fprintf(stderr, "%s: out of memory after first half\n", argv[0]);
     sieve_clear(&s);
     exit(1);
   }
   fprintf(stderr, "%s: half done ... \n", argv[0]);
   for(ix = 0; ix < s.nbits; ix++) {
     if(S_ISSET(&s, ix)) {
       p[cur] = S_VAL(&s, ix);
       printf("%ld\n", p[cur]);
       ++cur;
     }
   }
   sieve_reset(&s, p[cur - 1]);
   fprintf(stderr, "%s: crossing off %d found primes ... \n", argv[0], cur);
   for(ix = 0; ix < cur; ix++) {
     sieve_cross(&s, p[ix]);
     if(!(ix % 1000))
       fputc('.', stderr);
   }
   fputc('\n', stderr);
   free(p);
   fprintf(stderr, "%s: sieving again from %ld ... \n", argv[0], p[cur - 1]);
   c = 0;
   while((pr = sieve_next(&s)) > 0) {
     ++c;
   }
   fprintf(stderr, "%s: done!\n", argv[0]);
   for(ix = 0; ix < s.nbits; ix++) {
     if(S_ISSET(&s, ix)) {
       printf("%ld\n", S_VAL(&s, ix));
     }
   }
   sieve_clear(&s);
   return 0;
 }
 void sieve_init(sieve *sp, long base, int nbits)
 {
   sp->size = (nbits / CHAR_BIT);
   if(nbits % CHAR_BIT)
     ++sp->size;
   sp->bits = calloc(sp->size, sizeof(byte));
   memset(sp->bits, UCHAR_MAX, sp->size);
   if(!(base & 1))
     ++base;
   sp->base = base;
   sp->next = 0;
   sp->nbits = sp->size * CHAR_BIT;
 }
 void sieve_grow(sieve *sp, int nbits)
 {
   int  ns = (nbits / CHAR_BIT);
   if(nbits % CHAR_BIT)
     ++ns;
   if(ns > sp->size) {
     byte   *tmp;
     int     ix;
     tmp = calloc(ns, sizeof(byte));
     if(tmp == NULL) {
       fprintf(stderr, "Error: out of memory in sieve_grow\n");
       return;
     }
     memcpy(tmp, sp->bits, sp->size);
     for(ix = sp->size; ix < ns; ix++) {
       tmp[ix] = UCHAR_MAX;
     }
     free(sp->bits);
     sp->bits = tmp;
     sp->size = ns;
     sp->nbits = sp->size * CHAR_BIT;
   }
 }
 long sieve_next(sieve *sp)
 {
   long out;
   int  ix = 0;
   long val;
   if(sp->next > sp->nbits)
     return -1;
   out = S_VAL(sp, sp->next);
 #ifdef DEBUG
   fprintf(stderr, "Sieving %ld\n", out);
 #endif
   /* Sieve out all multiples of the current prime */
   val = out;
   while(ix < sp->nbits) {
     val += out;
     ix = S_BIT(sp, val);
     if((val & 1) && ix < sp->nbits) { /* && S_ISSET(sp, ix)) { */
       S_CLR(sp, ix);
 #ifdef DEBUG
       fprintf(stderr, "Crossing out %ld (bit %d)\n", val, ix);
 #endif
     }
   }
   /* Scan ahead to the next prime */
   ++sp->next;
   while(sp->next < sp->nbits && !S_ISSET(sp, sp->next))
     ++sp->next;
   return out;
 }
 void sieve_cross(sieve *sp, long val)
 {
   int  ix = 0;
   long cur = val;
   while(cur < sp->base)
     cur += val;
   ix = S_BIT(sp, cur);
   while(ix < sp->nbits) {
     if(cur & 1)
       S_CLR(sp, ix);
     cur += val;
     ix = S_BIT(sp, cur);
   }
 }
 void sieve_reset(sieve *sp, long base)
 {
   memset(sp->bits, UCHAR_MAX, sp->size);
   sp->base = base;
   sp->next = 0;
 }
 void sieve_clear(sieve *sp)
 {
   if(sp->bits)
     free(sp->bits);
   sp->bits = NULL;
 }

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security/nss/lib/freebl/mpi/utils/sieve.c@6474c204b198 (annotated)

security/nss/lib/freebl/mpi/utils/sieve.c