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Kevin Ryde 2005-03-13 00:29:04 +00:00
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/* srfi-60.c --- Integers as Bits
*
* Copyright (C) 2005 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <libguile.h>
#include "libguile/private-gc.h" /* for SCM_MIN */
#include "srfi-60.h"
SCM_DEFINE (scm_srfi60_log2_binary_factors, "log2-binary-factors", 1, 0, 0,
(SCM n),
"Return a count of how many factors of 2 are present in @var{n}.\n"
"This is also the bit index of the lowest 1 bit in @var{n}. If\n"
"@var{n} is 0, the return is @math{-1}.\n"
"\n"
"@example\n"
"(log2-binary-factors 6) @result{} 1\n"
"(log2-binary-factors -8) @result{} 3\n"
"@end example")
#define FUNC_NAME s_scm_srfi60_log2_binary_factors
{
SCM ret = SCM_EOL;
if (SCM_INUMP (n))
{
long nn = SCM_I_INUM (n);
if (nn == 0)
return SCM_I_MAKINUM (-1);
nn = nn ^ (nn-1); /* 1 bits for each low 0 and lowest 1 */
return scm_logcount (SCM_I_MAKINUM (nn >> 1));
}
else if (SCM_BIGP (n))
{
/* no need for scm_remember_upto_here_1 here, mpz_scan1 doesn't do
anything that could result in a gc */
return SCM_I_MAKINUM (mpz_scan1 (SCM_I_BIG_MPZ (n), 0L));
}
else
SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
return ret;
}
#undef FUNC_NAME
SCM_DEFINE (scm_srfi60_copy_bit, "copy-bit", 3, 0, 0,
(SCM index, SCM n, SCM bit),
"Return @var{n} with the bit at @var{index} set according to\n"
"@var{newbit}. @var{newbit} should be @code{#t} to set the bit\n"
"to 1, or @code{#f} to set it to 0. Bits other than at\n"
"@var{index} are unchanged in the return.\n"
"\n"
"@example\n"
"(copy-bit 1 #b0101 #t) @result{} 7\n"
"@end example")
#define FUNC_NAME s_scm_srfi60_copy_bit
{
SCM r;
unsigned long ii;
int bb;
ii = scm_to_ulong (index);
bb = scm_to_bool (bit);
if (SCM_INUMP (n))
{
long nn = SCM_INUM (n);
/* can't set high bit ii==SCM_LONG_BIT-1, that would change the sign,
which is not what's wanted */
if (ii < SCM_LONG_BIT-1)
{
nn &= ~(1L << ii); /* zap bit at index */
nn |= (bb << ii); /* insert desired bit */
return scm_from_long (nn);
}
else
{
/* bits at ii==SCM_LONG_BIT-1 and above are all copies of the sign
bit, if this is already the desired "bit" value then no need to
make a new bignum value */
if (bb == (nn < 0))
return n;
r = scm_i_long2big (nn);
goto big;
}
}
else if (SCM_BIGP (n))
{
/* if the bit is already what's wanted then no need to make a new
bignum */
if (bb == mpz_tstbit (SCM_I_BIG_MPZ (n), ii))
return n;
r = scm_i_clonebig (n, 1);
big:
if (bb)
mpz_setbit (SCM_I_BIG_MPZ (r), ii);
else
mpz_clrbit (SCM_I_BIG_MPZ (r), ii);
/* changing a high bit might put the result into range of a fixnum */
return scm_i_normbig (r);
}
else
SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
}
#undef FUNC_NAME
SCM_DEFINE (scm_srfi60_rotate_bit_field, "rotate-bit-field", 4, 0, 0,
(SCM n, SCM count, SCM start, SCM end),
"Return @var{n} with the bit field from @var{start} (inclusive)\n"
"to @var{end} (exclusive) rotated upwards by @var{count} bits.\n"
"\n"
"@var{count} can be positive or negative, and it can be more\n"
"than the field width (it'll be reduced modulo the width).\n"
"\n"
"@example\n"
"(rotate-bit-field #b0110 2 1 4) @result{} #b1010\n"
"@end example")
#define FUNC_NAME s_scm_srfi60_rotate_bit_field
{
unsigned long ss = scm_to_ulong (start);
unsigned long ee = scm_to_ulong (end);
unsigned long ww, cc;
SCM_ASSERT_RANGE (3, end, (ee >= ss));
ww = ee - ss;
cc = scm_to_ulong (scm_modulo (count, scm_difference (end, start)));
if (SCM_INUMP (n))
{
long nn = SCM_INUM (n);
if (ee <= SCM_LONG_BIT-1)
{
/* all within a long */
long below = nn & ((1L << ss) - 1); /* before start */
long above = nn & (-1L << ee); /* above end */
long fmask = (-1L << ss) & ((1L << ee) - 1); /* field mask */
long ff = nn & fmask; /* field */
return scm_from_long (above
| ((ff << cc) & fmask)
| ((ff >> (ww-cc)) & fmask)
| below);
}
else
{
/* either no movement, or a field of only 0 or 1 bits, result
unchanged, avoid creating a bignum */
if (cc == 0 || ww <= 1)
return n;
n = scm_i_long2big (nn);
goto big;
}
}
else if (SCM_BIGP (n))
{
mpz_t tmp;
SCM r;
/* either no movement, or in a field of only 0 or 1 bits, result
unchanged, avoid creating a new bignum */
if (cc == 0 || ww <= 1)
return n;
big:
r = scm_i_ulong2big (0);
mpz_init (tmp);
/* portion above end */
mpz_fdiv_q_2exp (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (n), ee);
mpz_mul_2exp (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), ee);
/* field high part, width-count bits from start go to start+count */
mpz_fdiv_q_2exp (tmp, SCM_I_BIG_MPZ (n), ss);
mpz_fdiv_r_2exp (tmp, tmp, ww - cc);
mpz_mul_2exp (tmp, tmp, ss + cc);
mpz_ior (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), tmp);
/* field high part, count bits from end-count go to start */
mpz_fdiv_q_2exp (tmp, SCM_I_BIG_MPZ (n), ee - cc);
mpz_fdiv_r_2exp (tmp, tmp, cc);
mpz_mul_2exp (tmp, tmp, ss);
mpz_ior (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), tmp);
/* portion below start */
mpz_fdiv_r_2exp (tmp, SCM_I_BIG_MPZ (n), ss);
mpz_ior (SCM_I_BIG_MPZ (r), SCM_I_BIG_MPZ (r), tmp);
mpz_clear (tmp);
/* bits moved around might leave us in range of an inum */
return scm_i_normbig (r);
}
else
SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
}
#undef FUNC_NAME
SCM_DEFINE (scm_srfi60_reverse_bit_field, "reverse-bit-field", 3, 0, 0,
(SCM n, SCM start, SCM end),
"Return @var{n} with the bits between @var{start} (inclusive) to\n"
"@var{end} (exclusive) reversed.\n"
"\n"
"@example\n"
"(reverse-bit-field #b101001 2 4) @result{} #b100101\n"
"@end example")
#define FUNC_NAME s_scm_srfi60_reverse_bit_field
{
long ss = scm_to_long (start);
long ee = scm_to_long (end);
long swaps = (ee - ss) / 2; /* number of swaps */
SCM b;
if (SCM_INUMP (n))
{
long nn = SCM_INUM (n);
if (ee <= SCM_LONG_BIT-1)
{
/* all within a long */
long smask = 1L << ss;
long emask = 1L << (ee-1);
for ( ; swaps > 0; swaps--)
{
long sbit = nn & smask;
long ebit = nn & emask;
nn ^= sbit ^ (ebit ? smask : 0) /* zap sbit, put ebit value */
^ ebit ^ (sbit ? emask : 0); /* zap ebit, put sbit value */
smask <<= 1;
emask >>= 1;
}
return scm_from_long (nn);
}
else
{
/* avoid creating a new bignum if reversing only 0 or 1 bits */
if (ee - ss <= 1)
return n;
b = scm_i_long2big (nn);
goto big;
}
}
else if (SCM_BIGP (n))
{
/* avoid creating a new bignum if reversing only 0 or 1 bits */
if (ee - ss <= 1)
return n;
b = scm_i_clonebig (n, 1);
big:
ee--;
for ( ; swaps > 0; swaps--)
{
int sbit = mpz_tstbit (SCM_I_BIG_MPZ (b), ss);
int ebit = mpz_tstbit (SCM_I_BIG_MPZ (b), ee);
if (sbit ^ ebit)
{
/* the two bits are different, flip them */
if (sbit)
{
mpz_clrbit (SCM_I_BIG_MPZ (b), ss);
mpz_setbit (SCM_I_BIG_MPZ (b), ee);
}
else
{
mpz_setbit (SCM_I_BIG_MPZ (b), ss);
mpz_clrbit (SCM_I_BIG_MPZ (b), ee);
}
}
ss++;
ee--;
}
/* swapping zero bits into the high might make us fit a fixnum */
return scm_i_normbig (b);
}
else
SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
}
#undef FUNC_NAME
SCM_DEFINE (scm_srfi60_integer_to_list, "integer->list", 1, 1, 0,
(SCM n, SCM len),
"Return bits from @var{n} in the form of a list of @code{#t} for\n"
"1 and @code{#f} for 0. The least significant @var{len} bits\n"
"are returned, and the first list element is the most\n"
"significant of those bits. If @var{len} is not given, the\n"
"default is @code{(integer-length @var{n})} (@pxref{Bitwise\n"
"Operations}).\n"
"\n"
"@example\n"
"(integer->list 6) @result{} (#t #t #f)\n"
"(integer->list 1 4) @result{} (#f #f #f #t)\n"
"@end example")
#define FUNC_NAME s_scm_srfi60_integer_to_list
{
SCM ret = SCM_EOL;
unsigned long ll, i;
if (SCM_UNBNDP (len))
len = scm_integer_length (n);
ll = scm_to_ulong (len);
if (SCM_INUMP (n))
{
long nn = SCM_I_INUM (n);
for (i = 0; i < ll; i++)
{
unsigned long shift = SCM_MIN (i, (unsigned long) SCM_LONG_BIT-1);
int bit = (nn >> shift) & 1;
ret = scm_cons (scm_from_bool (bit), ret);
}
}
else if (SCM_BIGP (n))
{
for (i = 0; i < ll; i++)
ret = scm_cons (scm_from_bool (mpz_tstbit (SCM_I_BIG_MPZ (n), i)),
ret);
scm_remember_upto_here_1 (n);
}
else
SCM_WRONG_TYPE_ARG (SCM_ARG1, n);
return ret;
}
#undef FUNC_NAME
SCM_DEFINE (scm_srfi60_list_to_integer, "list->integer", 1, 0, 0,
(SCM lst),
"Return an integer formed bitwise from the given @var{lst} list\n"
"of booleans. Each boolean is @code{#t} for a 1 and @code{#f}\n"
"for a 0. The first element becomes the most significant bit in\n"
"the return.\n"
"\n"
"@example\n"
"(list->integer '(#t #f #t #f)) @result{} 10\n"
"@end example")
#define FUNC_NAME s_scm_srfi60_list_to_integer
{
long len;
/* strip high zero bits from lst; after this the length tells us whether
an inum or bignum is required */
while (scm_is_pair (lst) && scm_is_false (SCM_CAR (lst)))
lst = SCM_CDR (lst);
SCM_VALIDATE_LIST_COPYLEN (SCM_ARG1, lst, len);
if (len <= SCM_I_FIXNUM_BIT - 1)
{
/* fits an inum (a positive inum) */
long n = 0;
while (scm_is_pair (lst))
{
n <<= 1;
if (! scm_is_false (SCM_CAR (lst)))
n++;
lst = SCM_CDR (lst);
}
return SCM_I_MAKINUM (n);
}
else
{
/* need a bignum */
SCM n = scm_i_ulong2big (0);
while (scm_is_pair (lst))
{
len--;
if (! scm_is_false (SCM_CAR (lst)))
mpz_setbit (SCM_I_BIG_MPZ (n), len);
lst = SCM_CDR (lst);
}
return n;
}
}
#undef FUNC_NAME
SCM_REGISTER_PROC (s_srfi60_booleans_to_integer, "booleans->integer", 0, 0, 1,
scm_srfi60_list_to_integer);
void
scm_init_srfi_60 (void)
{
#ifndef SCM_MAGIC_SNARFER
#include "srfi/srfi-60.x"
#endif
}

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;;; srfi-60.scm --- Integers as Bits
;; Copyright (C) 2005 Free Software Foundation, Inc.
;;
;; This library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public
;; License as published by the Free Software Foundation; either
;; version 2.1 of the License, or (at your option) any later version.
;;
;; This library is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public
;; License along with this library; if not, write to the Free Software
;; Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
(define-module (srfi srfi-60)
#:export (bitwise-and
bitwise-ior
bitwise-xor
bitwise-not
any-bits-set?
bit-count
bitwise-if bitwise-merge
log2-binary-factors first-set-bit
bit-set?
copy-bit
bit-field
copy-bit-field
arithmetic-shift
rotate-bit-field
reverse-bit-field
integer->list
list->integer
booleans->integer)
#:re-export (logand
logior
logxor
integer-length
logtest
logcount
logbit?
ash))
(load-extension "libguile-srfi-srfi-60-v-1" "scm_init_srfi_60")
(define bitwise-and logand)
(define bitwise-ior logior)
(define bitwise-xor logxor)
(define bitwise-not lognot)
(define any-bits-set? logtest)
(define bit-count logcount)
(define (bitwise-if mask n0 n1)
(logior (logand mask n0)
(logand (lognot mask) n1)))
(define bitwise-merge bitwise-if)
(define first-set-bit log2-binary-factors)
(define bit-set? logbit?)
(define bit-field bit-extract)
(define (copy-bit-field n newbits start end)
(logxor n (ash (logxor (bit-extract n start end) ;; cancel old
(bit-extract newbits 0 (- end start))) ;; insert new
start)))
(define arithmetic-shift ash)
(cond-expand-provide (current-module) '(srfi-60))