diff options
| -rw-r--r-- | ChangeLog | 10 | ||||
| -rw-r--r-- | arith.c | 40 | ||||
| -rw-r--r-- | arith.h | 1 | ||||
| -rw-r--r-- | eval.c | 1 | ||||
| -rw-r--r-- | txr.1 | 28 |
5 files changed, 80 insertions, 0 deletions
@@ -1,3 +1,13 @@ +2015-01-27 Kaz Kylheku <kaz@kylheku.com> + + * arith.c (width): New function. + + * arith.h (width): Declared. + + * eval.c (eval_init): Width registered as intrisinc. + + * txr.1: Documented width. + 2015-01-25 Kaz Kylheku <kaz@kylheku.com> * eval.c (call_f): New global variable. @@ -2187,6 +2187,46 @@ val toint(val obj, val base) } } +val width(val obj) +{ + switch (tag(obj)) { + case TAG_NUM: + case TAG_CHR: + { + cnum n = c_num(obj); + + if (n < 0) { + n &= INT_PTR_MAX; + n ^= INT_PTR_MAX; + return num_fast(highest_bit(n)); + } + return num_fast(highest_bit(n)); + } + case TAG_PTR: + if (type(obj) == BGNUM) { + int count; + if (mp_cmp_z(mp(obj)) == MP_LT) { + mp_int tmp; + int i; + + mp_2comp(mp(obj), &tmp, mp(obj)->used); + + for (i = 0; i < tmp.used; i++) + tmp.dp[i] ^= MP_DIGIT_MAX; + + count = mp_count_bits(&tmp); + mp_clear(&tmp); + } else { + count = mp_count_bits(mp(obj)); + } + return num(count); + } + default: + break; + } + uw_throwf(error_s, lit("integer-length: ~s isn't an integer"), obj, nao); +} + void arith_init(void) { mp_init(&NUM_MAX_MP); @@ -35,4 +35,5 @@ val n_choose_k(val n, val k); val n_perm_k(val n, val k); val tofloat(val obj); val toint(val obj, val base); +val width(val num); void arith_init(void); @@ -3851,6 +3851,7 @@ void eval_init(void) reg_fun(intern(lit("ash"), user_package), func_n2(ash)); reg_fun(intern(lit("bit"), user_package), func_n2(bit)); reg_fun(intern(lit("mask"), user_package), func_n0v(maskv)); + reg_fun(intern(lit("width"), user_package), func_n1(width)); reg_fun(intern(lit("regex-compile"), user_package), func_n2o(regex_compile, 1)); reg_fun(intern(lit("regexp"), user_package), func_n1(regexp)); @@ -19395,6 +19395,34 @@ In other words, the following equivalences hold: (mask a b c ...) <--> (logior (mask a) (mask b) (mask c) ...) .cble +.coNP Function @ width +.synb +.mets (width << integer *) +.syne +.desc +A two's complement representation of an integer consists of a sign bit and a +manitssa field. +The +.code width +function computes the minimum number of bits required for the mantissa portion +of the two's complement representation of the +.meta integer +argument. + +For a nonnegative argument, the width also corresponds to the number of bits +required for a natural binary representation of that value. + +Two integer values have a width of zero, namely 0 and -1. This means that these +two values can be represented in a one-bit two's complement, consisting of only +a sign bit: the one-bit two's complement bitfield 1 denotes -1, and 0 denotes +0. + +Similarly, two integer values have a width of 1: 1 and -2. The two-bit +two's complement bitfield 01 denotes 1, and 10 denotes -2. + +The argument may be a character. + + .SS* Exceptions .coNP Functions @, throw @ throwf and @ error .synb |