Spritz in C

spritz.c

// This file was written by TQ Hirsch <thequux@thequux.com>.

// It may be used under any of the following licenses, at your
// discretion:
//   - Public Domain
//   - WTFPLv2
//   - CC-0
//   - MIT
//   - ISC

// This file may be used as a header for separate compilation by
// #define-ing SPRITZ_HEADER_ONLY. Alternatively, cut this file at the
// line that contains "=== END HEADER ==="; the top half is usuable as
// a header while the bottom half contains the implementation. If you
// do this, the header should be called "spritz.h"

#ifndef SPRITZ__H
#define SPRITZ__H
#include <stdint.h> 

#ifdef __cplusplus
extern "C" {
#endif
  
typedef struct spritz_t {
  uint8_t s[256];
  uint8_t i,j,k,z,a,w;
} spritz_t;

#define SPRITZ_STATIC_INIT {			\
  {   0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15, 	\
     16,  17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,  30,  31,	\
     32,  33,  34,  35,  36,  37,  38,  39,  40,  41,  42,  43,  44,  45,  46,  47,	\
     48,  49,  50,  51,  52,  53,  54,  55,  56,  57,  58,  59,  60,  61,  62,  63,	\
     64,  65,  66,  67,  68,  69,  70,  71,  72,  73,  74,  75,  76,  77,  78,  79,	\
     80,  81,  82,  83,  84,  85,  86,  87,  88,  89,  90,  91,  92,  93,  94,  95,	\
     96,  97,  98,  99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111,	\
    112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127,	\
    128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143,	\
    144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159,	\
    160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175,	\
    176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191,	\
    192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207,	\
    208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223,	\
    224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239,	\
    240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255},	\
  0, 0, 0, 0, 0, 1}


void spritz_init(spritz_t *sp);
void spritz_absorb(spritz_t *sp, const uint8_t *buf, size_t len);
void spritz_absorb_stop(spritz_t *sp);
void spritz_squeeze(spritz_t *sp, const uint8_t *buf, size_t len);
#ifdef __cplusplus
}
#endif
#endif // !SPRITZ__H

// === END HEADER ===
// === BEGIN CODE ===
#ifndef SPRITZ_HEADER_ONLY
#ifndef SPRITZ__H
#include "spritz.h"
#endif

#ifdef __cplusplus
extern "C" {
#endif

#define S (sp->s)
#define I (sp->i)
#define J (sp->j)
#define K (sp->k)
#define Z (sp->z)
#define A (sp->a)
#define W (sp->w)
#define SWAP(a,b) do { uint8_t t = (a); (a) = (b); (b) = t; } while(0)

#define SPRITZ_ABS_NIBBLE(b) do {		\
    if (A == 128) spritz_shuffle(sp);		\
    SWAP(S[A], S[128 + ((b) & 0xF)]);		\
    A++;					\
  }
#define SPRITZ_UPDATE() do {			\
  I += W;					\
  J = K + S[J + S[I]];				\
  K = I + K + S[J];				\
  SWAP(S[I], S[J]);				\
  } while (0)
  
void spritz_init(spritz_t *sp) {
  int i;
  for (i = 0; i < 256; i++) {
    S[i] = (uint8_t)i;
  }
  I = J = K = Z = A = 0;
  W = 1;
}
  
void spritz_absorb(spritz_t *sp, const uint8_t *buf, size_t len) {
  int i;
  uint8_t b, t;
  for (i = 0; i < len; i++) {
    b = buf[i];
    SPRITZ_ABS_NIBBLE(b & 0xF);
    SPRITZ_ABS_NIBBLE(b >> 4);
  }
}

void spritz_absorb_stop(spritz_t *sp) {
  if (A == 128) spritz_shuffle(sp);
  A++;
}

void spritz_squeeze(spritz_t *sp, const uint8_t *buf, size_t len) {
  if (A > 0) spritz_shuffle(sp);
  int i;
  for (i = 0; i < len; i++) {
    SPRITZ_UPDATE();
    buf[i] = Z = S[J + S[I + S[Z+K]]];
  }
}

void spritz_whip(spritz_t *sp) {
  int i;
  for (i = 0; i < 512; i++) SPRITZ_UPDATE();
  w += 2;
}

void spritz_crush(spritz_t *sp) {
  int i;
  for (i = 0; i < 128; i++) {
    uint8_t a,b, m;
    a = S[i];
    b = S[255-i];
    // take high bit of (b-a), place it in the low bit, and negate it
    // (to sign extend)
    // in other words, m = (a < b) ? 0 : 0xff;
    m = ~(((b - a) & 0x80) >> 7) + 1;
    S[i] = a &~ m | b &  m;
    S[255-i] = a &  m | b &~ m;
  }
}

void spritz_shuffle(spritz_t *sp) {
  spritz_whip(sp);
  spritz_crush(sp);
  spritz_whip(sp);
  spritz_crush(sp);
  spritz_whip(sp);
  A = 0;
}
#ifdef __cplusplus
}
#endif
#endif // !SPRITZ_HEADER_ONLY