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Backport #5271

closed

Integer#round should never return a Float

Backport #5271: Integer#round should never return a Float

Added by marcandre (Marc-Andre Lafortune) about 15 years ago. Updated almost 15 years ago.

Status:
Closed
Assignee:
-
[ruby-core:39261]

Description

Integer#round sometimes returns... a float!

42.round(-1e9) # => 0.0

There's a check for out of range arguments, but it's not really needed and is machine dependent.

The following patch fixes the issue by optimizing for most cases and double checking for the rare extremely unlikely case where 10**ndigits does not fit in a bignum but num does and has almost ndigits digits.

Committed to trunk but would be nice to backport for Ruby 1.9.3.

diff --git a/numeric.c b/numeric.c
index 201dfab..a767fa5 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3320,6 +3320,7 @@ int_round(int argc, VALUE* argv, VALUE num)
{
VALUE n, f, h, r;
int ndigits;

  • long bytes;
    ID op;

    if (argc == 0) return num;
    @@ -3331,11 +3332,15 @@ int_round(int argc, VALUE* argv, VALUE num)
    if (ndigits == 0) {
    return num;
    }

  • ndigits = -ndigits;
  • if (ndigits < 0) {
  •   rb_raise(rb_eArgError, "ndigits out of range");
  • /* If 10**N / 2 > num, then return 0 */
  • /* We have log_256(10) > 0.415241 and log_256(1/2) = -0.125, so */
  • bytes = FIXNUM_P(num) ? sizeof(long) : rb_funcall(num, rb_intern("size"), 0);
  • if (-0.415241 * ndigits - 0.125 > bytes ) {
  •   return INT2FIX(0);
    }
  • f = int_pow(10, ndigits);
  • f = int_pow(10, -ndigits);
    if (FIXNUM_P(num) && FIXNUM_P(f)) {
    SIGNED_VALUE x = FIX2LONG(num), y = FIX2LONG(f);
    int neg = x < 0;
    @@ -3344,6 +3349,10 @@ int_round(int argc, VALUE* argv, VALUE num)
    if (neg) x = -x;
    return LONG2NUM(x);
    }
  • if (TYPE(f) == T_FLOAT) {
  •   /* then int_pow overflow */

  •   return INT2FIX(0);
  • }
    h = rb_funcall(f, '/', 1, INT2FIX(2));
    r = rb_funcall(num, '%', 1, f);
    n = rb_funcall(num, '-', 1, r);
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