srfi/srfi-60.c

   1 /* srfi-60.c --- Integers as Bits
   2  *
   3  * Copyright (C) 2005, 2006, 2008 Free Software Foundation, Inc.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2.1 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  18  */
  19
  20 #ifdef HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <libguile.h>
  25 #include <srfi/srfi-60.h>
  26
  27
  28 SCM_DEFINE (scm_srfi60_log2_binary_factors, "log2-binary-factors", 1, 0, 0,
  29             (SCM n),
  30             "Return a count of how many factors of 2 are present in @var{n}.\n"
  31             "This is also the bit index of the lowest 1 bit in @var{n}.  If\n"
  32             "@var{n} is 0, the return is @math{-1}.\n"
  33             "\n"
  34             "@example\n"
  35             "(log2-binary-factors 6) @result{} 1\n"
  36             "(log2-binary-factors -8) @result{} 3\n"
  37             "@end example")
  38 #define FUNC_NAME s_scm_srfi60_log2_binary_factors
  39 {
  40   SCM ret = SCM_EOL;
  41
  42   if (SCM_I_INUMP (n))
  43     {
  44       long nn = SCM_I_INUM (n);
  45       if (nn == 0)
  46         return SCM_I_MAKINUM (-1);
  47       nn = nn ^ (nn-1);  /* 1 bits for each low 0 and lowest 1 */
  48       return scm_logcount (SCM_I_MAKINUM (nn >> 1));
  49     }
  50   else if (SCM_BIGP (n))
  51     {
  52       /* no need for scm_remember_upto_here_1 here, mpz_scan1 doesn't do
  53          anything that could result in a gc */
  54       return SCM_I_MAKINUM (mpz_scan1 (SCM_I_BIG_MPZ (n), 0L));
  55     }
  56   else
  57     SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
  58
  59   return ret;
  60 }
  61 #undef FUNC_NAME
  62
  63
  64 SCM_DEFINE (scm_srfi60_copy_bit, "copy-bit", 3, 0, 0,
  65             (SCM index, SCM n, SCM bit),
  66             "Return @var{n} with the bit at @var{index} set according to\n"
  67             "@var{newbit}.  @var{newbit} should be @code{#t} to set the bit\n"
  68             "to 1, or @code{#f} to set it to 0.  Bits other than at\n"
  69             "@var{index} are unchanged in the return.\n"
  70             "\n"
  71             "@example\n"
  72             "(copy-bit 1 #b0101 #t) @result{} 7\n"
  73             "@end example")
  74 #define FUNC_NAME s_scm_srfi60_copy_bit
  75 {
  76   SCM r;
  77   unsigned long ii;
  78   int bb;
  79
  80   ii = scm_to_ulong (index);
  81   bb = scm_to_bool (bit);
  82
  83   if (SCM_I_INUMP (n))
  84     {
  85       long nn = SCM_I_INUM (n);
  86
  87       /* can't set high bit ii==SCM_LONG_BIT-1, that would change the sign,
  88          which is not what's wanted */
  89       if (ii < SCM_LONG_BIT-1)
  90         {
  91           nn &= ~(1L << ii);  /* zap bit at index */
  92           nn |= ((long) bb << ii);   /* insert desired bit */
  93           return scm_from_long (nn);
  94         }
  95       else
  96         {
  97           /* bits at ii==SCM_LONG_BIT-1 and above are all copies of the sign
  98              bit, if this is already the desired "bit" value then no need to
  99              make a new bignum value */
 100           if (bb == (nn < 0))
 101             return n;
 102
 103           r = scm_i_long2big (nn);
 104           goto big;
 105         }
 106     }
 107   else if (SCM_BIGP (n))
 108     {
 109       /* if the bit is already what's wanted then no need to make a new
 110          bignum */
 111       if (bb == mpz_tstbit (SCM_I_BIG_MPZ (n), ii))
 112         return n;
 113
 114       r = scm_i_clonebig (n, 1);
 115     big:
 116       if (bb)
 117         mpz_setbit (SCM_I_BIG_MPZ (r), ii);
 118       else
 119         mpz_clrbit (SCM_I_BIG_MPZ (r), ii);
 120
 121       /* changing a high bit might put the result into range of a fixnum */
 122       return scm_i_normbig (r);
 123     }
 124   else
 125     SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
 126 }
 127 #undef FUNC_NAME
 128
 129
 130 SCM_DEFINE (scm_srfi60_rotate_bit_field, "rotate-bit-field", 4, 0, 0,
 131             (SCM n, SCM count, SCM start, SCM end),
 132             "Return @var{n} with the bit field from @var{start} (inclusive)\n"
 133             "to @var{end} (exclusive) rotated upwards by @var{count} bits.\n"
 134             "\n"
 135             "@var{count} can be positive or negative, and it can be more\n"
 136             "than the field width (it'll be reduced modulo the width).\n"
 137             "\n"
 138             "@example\n"
 139             "(rotate-bit-field #b0110 2 1 4) @result{} #b1010\n"
 140             "@end example")
 141 #define FUNC_NAME s_scm_srfi60_rotate_bit_field
 142 {
 143   unsigned long ss = scm_to_ulong (start);
 144   unsigned long ee = scm_to_ulong (end);
 145   unsigned long ww, cc;
 146
 147   SCM_ASSERT_RANGE (3, end, (ee >= ss));
 148   ww = ee - ss;
 149
 150   cc = scm_to_ulong (scm_modulo (count, scm_difference (end, start)));
 151
 152   if (SCM_I_INUMP (n))
 153     {
 154       long nn = SCM_I_INUM (n);
 155
 156       if (ee <= SCM_LONG_BIT-1)
 157         {
 158           /* all within a long */
 159           long below = nn & ((1L << ss) - 1);  /* before start */
 160           long above = nn & (-1L << ee);       /* above end */
 161           long fmask = (-1L << ss) & ((1L << ee) - 1);  /* field mask */
 162           long ff = nn & fmask;                /* field */
 163
 164           return scm_from_long (above
 165                                 | ((ff << cc) & fmask)
 166                                 | ((ff >> (ww-cc)) & fmask)
 167                                 | below);
 168         }
 169       else
 170         {
 171           /* either no movement, or a field of only 0 or 1 bits, result
 172              unchanged, avoid creating a bignum */
 173           if (cc == 0 || ww <= 1)
 174             return n;
 175
 176           n = scm_i_long2big (nn);
 177           goto big;
 178         }
 179     }
 180   else if (SCM_BIGP (n))
 181     {
 182       mpz_t tmp;
 183       SCM r;
 184
 185       /* either no movement, or in a field of only 0 or 1 bits, result
 186          unchanged, avoid creating a new bignum */
 187       if (cc == 0 || ww <= 1)
 188         return n;
 189
 190     big:
 191       r = scm_i_ulong2big (0);
 192       mpz_init (tmp);
 193
 194       /* portion above end */
 195       mpz_fdiv_q_2exp (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (n), ee);
 196       mpz_mul_2exp (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), ee);
 197
 198       /* field high part, width-count bits from start go to start+count */
 199       mpz_fdiv_q_2exp (tmp, SCM_I_BIG_MPZ (n), ss);
 200       mpz_fdiv_r_2exp (tmp, tmp, ww - cc);
 201       mpz_mul_2exp (tmp, tmp, ss + cc);
 202       mpz_ior (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), tmp);
 203
 204       /* field high part, count bits from end-count go to start */
 205       mpz_fdiv_q_2exp (tmp, SCM_I_BIG_MPZ (n), ee - cc);
 206       mpz_fdiv_r_2exp (tmp, tmp, cc);
 207       mpz_mul_2exp (tmp, tmp, ss);
 208       mpz_ior (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), tmp);
 209
 210       /* portion below start */
 211       mpz_fdiv_r_2exp (tmp, SCM_I_BIG_MPZ (n), ss);
 212       mpz_ior (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), tmp);
 213
 214       mpz_clear (tmp);
 215
 216       /* bits moved around might leave us in range of an inum */
 217       return scm_i_normbig (r);
 218     }
 219   else
 220     SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
 221 }
 222 #undef FUNC_NAME
 223
 224
 225 SCM_DEFINE (scm_srfi60_reverse_bit_field, "reverse-bit-field", 3, 0, 0,
 226             (SCM n, SCM start, SCM end),
 227             "Return @var{n} with the bits between @var{start} (inclusive) to\n"
 228             "@var{end} (exclusive) reversed.\n"
 229             "\n"
 230             "@example\n"
 231             "(reverse-bit-field #b101001 2 4) @result{} #b100101\n"
 232             "@end example")
 233 #define FUNC_NAME s_scm_srfi60_reverse_bit_field
 234 {
 235   long ss = scm_to_long (start);
 236   long ee = scm_to_long (end);
 237   long swaps = (ee - ss) / 2;  /* number of swaps */
 238   SCM b;
 239
 240   if (SCM_I_INUMP (n))
 241     {
 242       long nn = SCM_I_INUM (n);
 243
 244       if (ee <= SCM_LONG_BIT-1)
 245         {
 246           /* all within a long */
 247           long smask = 1L << ss;
 248           long emask = 1L << (ee-1);
 249           for ( ; swaps > 0; swaps--)
 250             {
 251               long sbit = nn & smask;
 252               long ebit = nn & emask;
 253               nn ^= sbit ^ (ebit ? smask : 0)  /* zap sbit, put ebit value */
 254                 ^   ebit ^ (sbit ? emask : 0); /* zap ebit, put sbit value */
 255
 256               smask <<= 1;
 257               emask >>= 1;
 258             }
 259           return scm_from_long (nn);
 260         }
 261       else
 262         {
 263           /* avoid creating a new bignum if reversing only 0 or 1 bits */
 264           if (ee - ss <= 1)
 265             return n;
 266
 267           b = scm_i_long2big (nn);
 268           goto big;
 269         }
 270     }
 271   else if (SCM_BIGP (n))
 272     {
 273       /* avoid creating a new bignum if reversing only 0 or 1 bits */
 274       if (ee - ss <= 1)
 275         return n;
 276
 277       b = scm_i_clonebig (n, 1);
 278     big:
 279
 280       ee--;
 281       for ( ; swaps > 0; swaps--)
 282         {
 283           int sbit = mpz_tstbit (SCM_I_BIG_MPZ (b), ss);
 284           int ebit = mpz_tstbit (SCM_I_BIG_MPZ (b), ee);
 285           if (sbit ^ ebit)
 286             {
 287               /* the two bits are different, flip them */
 288               if (sbit)
 289                 {
 290                   mpz_clrbit (SCM_I_BIG_MPZ (b), ss);
 291                   mpz_setbit (SCM_I_BIG_MPZ (b), ee);
 292                 }
 293               else
 294                 {
 295                   mpz_setbit (SCM_I_BIG_MPZ (b), ss);
 296                   mpz_clrbit (SCM_I_BIG_MPZ (b), ee);
 297                 }
 298             }
 299           ss++;
 300           ee--;
 301         }
 302       /* swapping zero bits into the high might make us fit a fixnum */
 303       return scm_i_normbig (b);
 304     }
 305   else
 306     SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
 307 }
 308 #undef FUNC_NAME
 309
 310
 311 SCM_DEFINE (scm_srfi60_integer_to_list, "integer->list", 1, 1, 0,
 312             (SCM n, SCM len),
 313             "Return bits from @var{n} in the form of a list of @code{#t} for\n"
 314             "1 and @code{#f} for 0.  The least significant @var{len} bits\n"
 315             "are returned, and the first list element is the most\n"
 316             "significant of those bits.  If @var{len} is not given, the\n"
 317             "default is @code{(integer-length @var{n})} (@pxref{Bitwise\n"
 318             "Operations}).\n"
 319             "\n"
 320             "@example\n"
 321             "(integer->list 6)   @result{} (#t #t #f)\n"
 322             "(integer->list 1 4) @result{} (#f #f #f #t)\n"
 323             "@end example")
 324 #define FUNC_NAME s_scm_srfi60_integer_to_list
 325 {
 326   SCM ret = SCM_EOL;
 327   unsigned long ll, i;
 328
 329   if (SCM_UNBNDP (len))
 330     len = scm_integer_length (n);
 331   ll = scm_to_ulong (len);
 332
 333   if (SCM_I_INUMP (n))
 334     {
 335       long nn = SCM_I_INUM (n);
 336       for (i = 0; i < ll; i++)
 337         {
 338           unsigned long shift =
 339             (i < ((unsigned long) SCM_LONG_BIT-1))
 340             ? i : ((unsigned long) SCM_LONG_BIT-1);
 341           int bit = (nn >> shift) & 1;
 342           ret = scm_cons (scm_from_bool (bit), ret);
 343         }
 344     }
 345   else if (SCM_BIGP (n))
 346     {
 347       for (i = 0; i < ll; i++)
 348         ret = scm_cons (scm_from_bool (mpz_tstbit (SCM_I_BIG_MPZ (n), i)),
 349                         ret);
 350       scm_remember_upto_here_1 (n);
 351     }
 352   else
 353     SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
 354
 355   return ret;
 356 }
 357 #undef FUNC_NAME
 358
 359
 360 SCM_DEFINE (scm_srfi60_list_to_integer, "list->integer", 1, 0, 0,
 361             (SCM lst),
 362             "Return an integer formed bitwise from the given @var{lst} list\n"
 363             "of booleans.  Each boolean is @code{#t} for a 1 and @code{#f}\n"
 364             "for a 0.  The first element becomes the most significant bit in\n"
 365             "the return.\n"
 366             "\n"
 367             "@example\n"
 368             "(list->integer '(#t #f #t #f)) @result{} 10\n"
 369             "@end example")
 370 #define FUNC_NAME s_scm_srfi60_list_to_integer
 371 {
 372   long len;
 373
 374   /* strip high zero bits from lst; after this the length tells us whether
 375      an inum or bignum is required */
 376   while (scm_is_pair (lst) && scm_is_false (SCM_CAR (lst)))
 377     lst = SCM_CDR (lst);
 378
 379   SCM_VALIDATE_LIST_COPYLEN (SCM_ARG1, lst, len);
 380
 381   if (len <= SCM_I_FIXNUM_BIT - 1)
 382     {
 383       /* fits an inum (a positive inum) */
 384       long n = 0;
 385       while (scm_is_pair (lst))
 386         {
 387           n <<= 1;
 388           if (! scm_is_false (SCM_CAR (lst)))
 389             n++;
 390           lst = SCM_CDR (lst);
 391         }
 392       return SCM_I_MAKINUM (n);
 393     }
 394   else
 395     {
 396       /* need a bignum */
 397       SCM n = scm_i_ulong2big (0);
 398       while (scm_is_pair (lst))
 399         {
 400           len--;
 401           if (! scm_is_false (SCM_CAR (lst)))
 402             mpz_setbit (SCM_I_BIG_MPZ (n), len);
 403           lst = SCM_CDR (lst);
 404         }
 405       return n;
 406     }
 407 }
 408 #undef FUNC_NAME
 409
 410
 411 /* note: don't put "scm_srfi60_list_to_integer" arg on its own line, a
 412    newline breaks the snarfer */
 413 SCM_REGISTER_PROC (s_srfi60_booleans_to_integer, "booleans->integer", 0, 0, 1, scm_srfi60_list_to_integer);
 414
 415
 416 void
 417 scm_init_srfi_60 (void)
 418 {
 419 #ifndef SCM_MAGIC_SNARFER
 420 #include "srfi/srfi-60.x"
 421 #endif
 422 }