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mruby-numeric-ext: add Integer#bit_length

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Implement Integer#bit_length in mrbgems/mruby-numeric-ext.
- Fixnum: zero returns 0; negatives follow ~self rule; count bits by shifts.
- Bigint (MRB_USE_BIGINT): handle sign; negatives via mrb_bint_rev, then bit
  length via length of mrb_bint_to_s(..., 2).
- Add tests in mrbgems/mruby-numeric-ext/test/numeric.rb.
- Update README with examples.

Co-authored-by: Codex CLI <codex@openai.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-08-13 13:34:17 +09:00
parent 6e84066a42
commit e60acfc6ff
3 changed files with 62 additions and 0 deletions
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mrbgems/mruby-numeric-ext/src/numeric_ext.c
+36
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@@ -1,6 +1,7 @@
#include <mruby.h>
#include <mruby/numeric.h>
#include <mruby/array.h>
#include <mruby/string.h>
#include <mruby/internal.h>
#include <mruby/presym.h>
@@ -8,6 +9,40 @@
static mrb_value flo_remainder(mrb_state *mrb, mrb_value self);
#endif
/*
* call-seq:
* int.bit_length -> integer
*
* Returns the number of bits of the absolute value of self in binary representation.
* For zero, returns 0. For negative integers, behaves as (~self).bit_length
* (e.g., (-1).bit_length => 0, (-2).bit_length => 1).
*/
static mrb_value
int_bit_length(mrb_state *mrb, mrb_value self)
{
#ifdef MRB_USE_BIGINT
if (mrb_bigint_p(self)) {
mrb_int sign = mrb_bint_sign(mrb, self);
if (sign == 0) return mrb_fixnum_value(0);
mrb_value v = self;
if (sign < 0) v = mrb_bint_rev(mrb, self); /* ~self = -self-1 */
mrb_value s = mrb_bint_to_s(mrb, v, 2);
return mrb_int_value(mrb, (mrb_int)RSTRING_LEN(s));
}
#endif
mrb_int x = mrb_integer(self);
if (x == 0) return mrb_fixnum_value(0);
/* for negative fixnums, use ~x */
mrb_uint ux = (mrb_uint)(x < 0 ? ~x : x);
mrb_int bits = 0;
while (ux) {
bits++;
ux >>= 1;
}
return mrb_int_value(mrb, bits);
}
/*
* call-seq:
* num.remainder(numeric) -> real
@@ -435,6 +470,7 @@ mrb_mruby_numeric_ext_gem_init(mrb_state* mrb)
mrb_define_method_id(mrb, ic, MRB_SYM(pow), int_powm, MRB_ARGS_ARG(1,1));
mrb_define_method_id(mrb, ic, MRB_SYM(digits), int_digits, MRB_ARGS_OPT(1));
mrb_define_method_id(mrb, ic, MRB_SYM(size), int_size, MRB_ARGS_NONE());
mrb_define_method_id(mrb, ic, MRB_SYM(bit_length), int_bit_length, MRB_ARGS_NONE());
mrb_define_method_id(mrb, ic, MRB_SYM_Q(odd), int_odd, MRB_ARGS_NONE());
mrb_define_method_id(mrb, ic, MRB_SYM_Q(even), int_even, MRB_ARGS_NONE());
mrb_define_method_id(mrb, ic, MRB_SYM(gcd), int_gcd, MRB_ARGS_REQ(1));