89 lines
1.8 KiB
C
89 lines
1.8 KiB
C
#include "mupdf/fitz.h"
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/* The pseudo-random number generator in this file is based on the MIT licensed
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* implementation in musl libc. */
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#include <string.h>
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/* The seed is initialized in context.c as follows:
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* static uint16_t __seed48[7] = { 0, 0, 0, 0xe66d, 0xdeec, 0x5, 0xb };
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*/
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static uint64_t fz_rand48_step(uint16_t *xi, uint16_t *lc)
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{
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uint64_t a, x;
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x = xi[0] | (xi[1]+0U)<<16 | (xi[2]+0ULL)<<32;
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a = lc[0] | (lc[1]+0U)<<16 | (lc[2]+0ULL)<<32;
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x = a*x + lc[3];
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xi[0] = x;
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xi[1] = x>>16;
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xi[2] = x>>32;
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return x & 0xffffffffffffull;
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}
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double fz_erand48(fz_context *ctx, uint16_t s[3])
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{
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union {
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uint64_t u;
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double f;
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} x = { 0x3ff0000000000000ULL | fz_rand48_step(s, ctx->seed48+3)<<4 };
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return x.f - 1.0;
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}
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/*
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Pseudo-random numbers using a linear congruential algorithm and 48-bit
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integer arithmetic.
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*/
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double fz_drand48(fz_context *ctx)
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{
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return fz_erand48(ctx, ctx->seed48);
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}
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int32_t fz_nrand48(fz_context *ctx, uint16_t s[3])
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{
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return fz_rand48_step(s, ctx->seed48+3) >> 17;
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}
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int32_t fz_lrand48(fz_context *ctx)
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{
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return fz_nrand48(ctx, ctx->seed48);
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}
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int32_t fz_jrand48(fz_context *ctx, uint16_t s[3])
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{
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return (int32_t)(fz_rand48_step(s, ctx->seed48+3) >> 16);
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}
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int32_t fz_mrand48(fz_context *ctx)
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{
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return fz_jrand48(ctx, ctx->seed48);
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}
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void fz_lcong48(fz_context *ctx, uint16_t p[7])
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{
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memcpy(ctx->seed48, p, sizeof ctx->seed48);
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}
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uint16_t *fz_seed48(fz_context *ctx, uint16_t *s)
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{
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static uint16_t p[3];
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memcpy(p, ctx->seed48, sizeof p);
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memcpy(ctx->seed48, s, sizeof p);
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return p;
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}
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void fz_srand48(fz_context *ctx, int32_t seed)
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{
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uint16_t p[3] = { 0x330e, seed, seed>>16 };
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fz_seed48(ctx, p);
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}
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/*
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Fill block with len bytes of pseudo-randomness.
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*/
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void fz_memrnd(fz_context *ctx, unsigned char *data, int len)
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{
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while (len-- > 0)
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*data++ = (unsigned char)fz_lrand48(ctx);
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}
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