diff options
| -rw-r--r-- | ChangeLog | 10 | ||||
| -rw-r--r-- | arith.c | 13 | ||||
| -rw-r--r-- | eval.c | 2 | ||||
| -rw-r--r-- | lib.h | 2 | ||||
| -rw-r--r-- | txr.1 | 59 |
5 files changed, 86 insertions, 0 deletions
@@ -1,5 +1,15 @@ 2014-11-20 Kaz Kylheku <kaz@kylheku.com> + * arith.c (wrap_star, wrap): New functions. + + * eval.c (eval_init): Registered wrap and wrap* intrinsics. + + * lib.h (wrap_star, wrap): Declared. + + * txr.1: wrap and wrap* documented. + +2014-11-20 Kaz Kylheku <kaz@kylheku.com> + * arith.c (succ, ssucc, sssucc, pred, ppred, pppred): New functions. * eval.c (eval_init): Register new functions as intrinsics. @@ -938,6 +938,19 @@ divzero: uw_throw(numeric_error_s, lit("mod: division by zero")); } +val wrap_star(val start, val end, val num) +{ + val modulus = minus(end, start); + val num_off = minus(num, start); + val num_mod = mod(num_off, modulus); + return plus(start, num_mod); +} + +val wrap(val start, val end, val num) +{ + return wrap_star(start, succ(end), num); +} + static val to_float(val func, val num) { switch (type(num)) { @@ -3677,6 +3677,8 @@ void eval_init(void) reg_fun(intern(lit("abs"), user_package), func_n1(abso)); reg_fun(intern(lit("trunc"), user_package), func_n2(trunc)); reg_fun(intern(lit("mod"), user_package), func_n2(mod)); + reg_fun(intern(lit("wrap"), user_package), func_n3(wrap)); + reg_fun(intern(lit("wrap*"), user_package), func_n3(wrap_star)); reg_fun(intern(lit("/"), user_package), func_n2o(divi, 1)); reg_fun(intern(lit("expt"), user_package), func_n0v(exptv)); reg_fun(intern(lit("exptmod"), user_package), func_n3(exptmod)); @@ -538,6 +538,8 @@ val mul(val anum, val bnum); val mulv(val nlist); val trunc(val anum, val bnum); val mod(val anum, val bnum); +val wrap_star(val start, val end, val num); +val wrap(val start, val end, val num); val divi(val anum, val bnum); val zerop(val num); val evenp(val num); @@ -18035,6 +18035,65 @@ then generalized into the floating point domain. For instance the expression yields a residue of 0.25 because 0.5 "goes into" 0.75 only once, with a "remainder" of 0.25. +.coNP Functions @ wrap and @ wrap* +.synb +.mets (wrap < start < end << number ) +.mets (wrap < start < end << number ) +.syne +.desc +The +.code wrap +and +.code wrap* +functions reduce +.meta number +into the range specified by +.meta start +and +.metn end . + +Under +.code wrap +the range is inclusive of the +.meta end +value, whereas under +.code wrap* +it is exclusive. + +The following equivalence holds + +.cblk + (wrap a b c) <--> (wrap* a (succ b) c) +.cble + +The expression +.code (wrap* x0 x1 x) +performs the following calculation: + +.cblk +.meti (+ (mod (- x x0) (- x1 x0)) x0) +.cble + +In other words, first +.meta start +is subtracted from +.metn number . +Then the result is reduced modulo the displacement +between +.code start +and +.codn end . +Finally, +.meta start +is added back to that result, which is returned. + +.TP* Example: + +.cblk + ;; perform ROT13 on the string "nop" + [mapcar (opip (+ 13) (wrap #\ea #\ez)) "nop"] -> "abc" +.cble + .coNP Functions @ gcd and @ lcm .synb .mets (gcd << number *) |