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Rewrite 'rationalize' to fix bugs and improve efficiency.

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Fixes <http://bugs.gnu.org/14905>.
Reported by Göran Weinholt <goran@weinholt.se>.

* libguile/numbers.c (scm_rationalize): Rewrite.  Previously an
  incorrect algorithm was used which failed in many cases.

* test-suite/tests/numbers.test (rationalize): Add tests.
This commit is contained in:
Mark H Weaver 2013-07-20 12:29:02 -04:00
parent 824b9ad8b7
commit 620c13e8fc
2 changed files with 203 additions and 73 deletions
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29
test-suite/tests/numbers.test
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@ -1431,6 +1431,35 @@
(pass-if (eqv? 1/3 (rationalize 3/10 -1/10)))
(pass-if (eqv? -1/3 (rationalize -3/10 -1/10)))
;; Prior to Guile 2.0.10, rationalize used a faulty algorithm that
;; incorrectly returned 2/3 and -2/3 in the following cases.
(pass-if (eqv? 1/2 (rationalize #e+0.67 1/4)))
(pass-if (eqv? -1/2 (rationalize #e-0.67 1/4)))
(pass-if (eqv? 1 (rationalize #e+0.67 1/3)))
(pass-if (eqv? -1 (rationalize #e-0.67 1/3)))
(pass-if (eqv? 1/2 (rationalize #e+0.66 1/3)))
(pass-if (eqv? -1/2 (rationalize #e-0.66 1/3)))
(pass-if (eqv? 1 (rationalize #e+0.67 2/3)))
(pass-if (eqv? -1 (rationalize #e-0.67 2/3)))
(pass-if (eqv? 0 (rationalize #e+0.66 2/3)))
(pass-if (eqv? 0 (rationalize #e-0.66 2/3)))
;; Prior to Guile 2.0.10, rationalize used a faulty algorithm that
;; incorrectly computed the following approximations of PI.
(with-test-prefix "pi"
(define *pi* #e3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679)
(pass-if (eqv? 16/5 (rationalize *pi* 1/10)))
(pass-if (eqv? 201/64 (rationalize *pi* 1/1000)))
(pass-if (eqv? 75948/24175 (rationalize *pi* (expt 10 -7))))
(pass-if (eqv? 100798/32085 (rationalize *pi* (expt 10 -8))))
(pass-if (eqv? 58466453/18610450 (rationalize *pi* (expt 10 -14))))
(pass-if (eqv? 2307954651196778721982809475299879198775111361078/734644782339796933783743757007944508986600750685
(rationalize *pi* (expt 10 -95)))))
(pass-if (test-eqv? (/ 1.0 3) (rationalize 0.3 1/10)))
(pass-if (test-eqv? (/ -1.0 3) (rationalize -0.3 1/10)))
(pass-if (test-eqv? (/ 1.0 3) (rationalize 0.3 -1/10)))