src/gf.h

   1 /*
   2  * transsip - the telephony toolkit
   3  * By Daniel Borkmann <daniel@transsip.org>
   4  * Copyright 2012 Daniel Borkmann <dborkma@tik.ee.ethz.ch>
   5  * Subject to the GPL, version 2.
   6  * Based on Bhaskar Biswas and Nicolas Sendrier McEliece
   7  * implementation, LGPL 2.1.
   8  */
   9
  10 #ifndef GF_H
  11 #define GF_H
  12
  13 #include <stdint.h>
  14
  15 typedef uint16_t gf16_t;
  16
  17 extern uint32_t gf_extension_degree, gf_cardinality, gf_multiplicative_order;
  18 extern gf16_t *gf_log_t, *gf_exp_t;
  19
  20 #define gf_extd()               gf_extension_degree
  21 #define gf_card()               gf_cardinality
  22 #define gf_ord()                gf_multiplicative_order
  23
  24 #define gf_unit()               1
  25 #define gf_zero()               0
  26
  27 #define gf_add(x, y)            ((x) ^ (y))
  28 #define gf_sub(x, y)            ((x) ^ (y))
  29 #define gf_exp(i)               gf_exp_t[i] /* alpha^i */
  30 #define gf_log(x)               gf_log_t[x] /* return i when x=alpha^i */
  31
  32 #define gf_zdo(t, func)         (!!(t) ? (func) : 0)
  33
  34 /**
  35  * residual modulo q-1
  36  *  when -q < d < 0, we get (q-1+d)
  37  *  when 0 <= d < q, we get (d)
  38  *  when q <= d < 2q-1, we get (d-q+1)
  39  * we obtain a value between 0 and (q-1) included, the class of 0 is
  40  * represented by 0 or q-1 (this is why we write
  41  * _K->exp[q-1] = _K->exp[0] = 1)
  42  */
  43 #define _gf_modq_1(d)           (((d) & gf_ord()) + ((d) >> gf_extd()))
  44
  45 #define gf_mul_fast(x, y)       gf_zdo(y, gf_exp(_gf_modq_1(gf_log(x) + gf_log(y))))
  46 #define gf_mul(x, y)            gf_zdo(x, gf_mul_fast(x, y))
  47 #define gf_square(x)            gf_zdo(x, gf_exp(_gf_modq_1(gf_log(x) << 1)))
  48 #define gf_sqrt(x)              gf_zdo(x, gf_exp(_gf_modq_1(gf_log(x) << (gf_extd() - 1))))
  49 #define gf_div(x, y)            gf_zdo(x, gf_exp(_gf_modq_1(gf_log(x) - gf_log(y))))
  50 #define gf_inv(x)               gf_exp(gf_ord() - gf_log(x))
  51
  52 extern void gf_init(int extdeg);
  53 extern gf16_t gf_rand(int (*rnd_u8)(void));
  54 extern gf16_t gf_pow(gf16_t x, int i);
  55
  56 #endif /* GF_H */