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Initial checkin of a portable framework for writing small GUI puzzle
games. [originally from svn r4138]
This commit is contained in:
Simon Tatham
282
random.c
Normal file
282
random.c
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/*
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* random.c: Internal random number generator, guaranteed to work
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* the same way on all platforms. Used when generating an initial
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* game state from a random game seed; required to ensure that game
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* seeds can be exchanged between versions of a puzzle compiled for
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* different platforms.
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*
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* The generator is based on SHA-1. This is almost certainly
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* overkill, but I had the SHA-1 code kicking around and it was
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* easier to reuse it than to do anything else!
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*/
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#include <assert.h>
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#include "puzzles.h"
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typedef unsigned long uint32;
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typedef struct {
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uint32 h[5];
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unsigned char block[64];
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int blkused;
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uint32 lenhi, lenlo;
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} SHA_State;
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/* ----------------------------------------------------------------------
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* Core SHA algorithm: processes 16-word blocks into a message digest.
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*/
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#define rol(x,y) ( ((x) << (y)) | (((uint32)x) >> (32-y)) )
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static void SHA_Core_Init(uint32 h[5])
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{
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h[0] = 0x67452301;
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h[1] = 0xefcdab89;
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h[2] = 0x98badcfe;
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h[3] = 0x10325476;
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h[4] = 0xc3d2e1f0;
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}
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static void SHATransform(uint32 * digest, uint32 * block)
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{
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uint32 w[80];
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uint32 a, b, c, d, e;
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int t;
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for (t = 0; t < 16; t++)
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w[t] = block[t];
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for (t = 16; t < 80; t++) {
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uint32 tmp = w[t - 3] ^ w[t - 8] ^ w[t - 14] ^ w[t - 16];
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w[t] = rol(tmp, 1);
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}
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a = digest[0];
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b = digest[1];
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c = digest[2];
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d = digest[3];
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e = digest[4];
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for (t = 0; t < 20; t++) {
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uint32 tmp =
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rol(a, 5) + ((b & c) | (d & ~b)) + e + w[t] + 0x5a827999;
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e = d;
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d = c;
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c = rol(b, 30);
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b = a;
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a = tmp;
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}
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for (t = 20; t < 40; t++) {
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uint32 tmp = rol(a, 5) + (b ^ c ^ d) + e + w[t] + 0x6ed9eba1;
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e = d;
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d = c;
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c = rol(b, 30);
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b = a;
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a = tmp;
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}
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for (t = 40; t < 60; t++) {
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uint32 tmp = rol(a,
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5) + ((b & c) | (b & d) | (c & d)) + e + w[t] +
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0x8f1bbcdc;
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e = d;
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d = c;
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c = rol(b, 30);
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b = a;
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a = tmp;
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}
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for (t = 60; t < 80; t++) {
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uint32 tmp = rol(a, 5) + (b ^ c ^ d) + e + w[t] + 0xca62c1d6;
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e = d;
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d = c;
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c = rol(b, 30);
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b = a;
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a = tmp;
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}
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digest[0] += a;
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digest[1] += b;
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digest[2] += c;
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digest[3] += d;
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digest[4] += e;
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}
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/* ----------------------------------------------------------------------
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* Outer SHA algorithm: take an arbitrary length byte string,
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* convert it into 16-word blocks with the prescribed padding at
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* the end, and pass those blocks to the core SHA algorithm.
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*/
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static void SHA_Init(SHA_State * s)
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{
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SHA_Core_Init(s->h);
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s->blkused = 0;
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s->lenhi = s->lenlo = 0;
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}
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static void SHA_Bytes(SHA_State * s, void *p, int len)
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{
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unsigned char *q = (unsigned char *) p;
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uint32 wordblock[16];
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uint32 lenw = len;
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int i;
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/*
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* Update the length field.
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*/
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s->lenlo += lenw;
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s->lenhi += (s->lenlo < lenw);
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if (s->blkused && s->blkused + len < 64) {
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/*
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* Trivial case: just add to the block.
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*/
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memcpy(s->block + s->blkused, q, len);
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s->blkused += len;
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} else {
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/*
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* We must complete and process at least one block.
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*/
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while (s->blkused + len >= 64) {
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memcpy(s->block + s->blkused, q, 64 - s->blkused);
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q += 64 - s->blkused;
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len -= 64 - s->blkused;
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/* Now process the block. Gather bytes big-endian into words */
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for (i = 0; i < 16; i++) {
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wordblock[i] =
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(((uint32) s->block[i * 4 + 0]) << 24) |
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(((uint32) s->block[i * 4 + 1]) << 16) |
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(((uint32) s->block[i * 4 + 2]) << 8) |
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(((uint32) s->block[i * 4 + 3]) << 0);
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}
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SHATransform(s->h, wordblock);
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s->blkused = 0;
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}
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memcpy(s->block, q, len);
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s->blkused = len;
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}
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}
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static void SHA_Final(SHA_State * s, unsigned char *output)
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{
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int i;
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int pad;
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unsigned char c[64];
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uint32 lenhi, lenlo;
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if (s->blkused >= 56)
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pad = 56 + 64 - s->blkused;
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else
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pad = 56 - s->blkused;
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lenhi = (s->lenhi << 3) | (s->lenlo >> (32 - 3));
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lenlo = (s->lenlo << 3);
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memset(c, 0, pad);
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c[0] = 0x80;
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SHA_Bytes(s, &c, pad);
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c[0] = (lenhi >> 24) & 0xFF;
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c[1] = (lenhi >> 16) & 0xFF;
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c[2] = (lenhi >> 8) & 0xFF;
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c[3] = (lenhi >> 0) & 0xFF;
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c[4] = (lenlo >> 24) & 0xFF;
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c[5] = (lenlo >> 16) & 0xFF;
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c[6] = (lenlo >> 8) & 0xFF;
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c[7] = (lenlo >> 0) & 0xFF;
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SHA_Bytes(s, &c, 8);
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for (i = 0; i < 5; i++) {
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output[i * 4] = (s->h[i] >> 24) & 0xFF;
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output[i * 4 + 1] = (s->h[i] >> 16) & 0xFF;
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output[i * 4 + 2] = (s->h[i] >> 8) & 0xFF;
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output[i * 4 + 3] = (s->h[i]) & 0xFF;
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}
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}
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static void SHA_Simple(void *p, int len, unsigned char *output)
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{
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SHA_State s;
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SHA_Init(&s);
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SHA_Bytes(&s, p, len);
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SHA_Final(&s, output);
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}
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/* ----------------------------------------------------------------------
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* The random number generator.
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*/
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struct random_state {
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unsigned char seedbuf[40];
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unsigned char databuf[20];
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int pos;
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};
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random_state *random_init(char *seed, int len)
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{
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random_state *state;
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state = snew(random_state);
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SHA_Simple(seed, len, state->seedbuf);
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SHA_Simple(state->seedbuf, 20, state->seedbuf + 20);
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SHA_Simple(state->seedbuf, 40, state->databuf);
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state->pos = 0;
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return state;
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}
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unsigned long random_bits(random_state *state, int bits)
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{
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int ret = 0;
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int n;
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for (n = 0; n < bits; n += 8) {
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if (state->pos >= 20) {
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int i;
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for (i = 0; i < 20; i++) {
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if (state->seedbuf[i] != 0xFF) {
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state->seedbuf[i]++;
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break;
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} else
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state->seedbuf[i] = 0;
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}
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SHA_Simple(state->seedbuf, 40, state->databuf);
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state->pos = 0;
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}
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ret = (ret << 8) | state->databuf[state->pos++];
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}
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ret &= (1 << bits) - 1;
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return ret;
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}
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unsigned long random_upto(random_state *state, unsigned long limit)
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{
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int bits = 0;
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unsigned long max, divisor, data;
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while ((limit >> bits) != 0)
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bits++;
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bits += 3;
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assert(bits < 32);
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max = 1 << bits;
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divisor = max / limit;
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max = limit * divisor;
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do {
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data = random_bits(state, bits);
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} while (data >= max);
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return data / divisor;
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}
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void random_free(random_state *state)
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{
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sfree(state);
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}
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