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Fix rounding in scm_i_divide2double for negative arguments.

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* libguile/numbers.c (INUM_LOSSLESSLY_CONVERTIBLE_TO_DOUBLE):
  New macro.
  (scm_i_divide2double): Use INUM_LOSSLESSLY_CONVERTIBLE_TO_DOUBLE to
  determine if our fast path is safe.  Previously, negative arguments
  were not checked properly.

* test-suite/tests/numbers.test (exact->inexact): Add tests.
This commit is contained in:
Mark H Weaver 2013-07-16 00:00:23 -04:00
parent 7e8166f5bd
commit 4cc2e41cf7
2 changed files with 24 additions and 4 deletions
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13
test-suite/tests/numbers.test
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@ -4021,6 +4021,19 @@
(let ((big (ash 1 4096)))
(= 1.0 (exact->inexact (/ (1+ big) big)))))
;; In guile 2.0.9, 'exact->inexact' guaranteed proper rounding when
;; applied to non-negative fractions, but on 64-bit systems would
;; sometimes double-round when applied to negative fractions,
;; specifically when the numerator was a fixnum not exactly
;; representable as a double.
(with-test-prefix "frac inum/inum, numerator not exactly representable as a double"
(let ((n (+ 1 (expt 2 dbl-mant-dig))))
(for-each (lambda (d)
(test (/ n d)
(/ n d)
(exact->inexact (/ n d))))
'(3 5 6 7 9 11 13 17 19 23 0.0 -0.0 +nan.0 +inf.0 -inf.0))))
(test "round up to odd"
;; =====================================================
;; 11111111111111111111111111111111111111111111111111000101 ->