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[Guile-commits] 01/02: Fix 'round-ash' of negative integers by huge righ
From: |
Mark H. Weaver |
Subject: |
[Guile-commits] 01/02: Fix 'round-ash' of negative integers by huge right shift counts. |
Date: |
Sun, 14 Oct 2018 05:38:49 -0400 (EDT) |
mhw pushed a commit to branch stable-2.2
in repository guile.
commit 9448a078b5a35fc49a16d32c0398d5789a863f09
Author: Mark H Weaver <address@hidden>
Date: Sun Oct 14 05:24:14 2018 -0400
Fix 'round-ash' of negative integers by huge right shift counts.
This is a followup to commit 011aec7e240ef987931548d90c53e6692c85d01c.
When rounding, right shifting a negative integer by a huge shift count
results in 0, not -1.
* libguile/numbers.c: Add top-level 'verify' to ensure that the
assumptions in 'scm_ash' and 'scm_round_ash' are valid.
(scm_round_ash): In the case that handles huge right shifts, require
that the shift count _exceeds_ the integer length, and return 0 instead
of -1.
* test-suite/tests/numbers.test: Adjust tests accordingly.
---
libguile/numbers.c | 16 ++++++++++------
test-suite/tests/numbers.test | 10 +++++-----
2 files changed, 15 insertions(+), 11 deletions(-)
diff --git a/libguile/numbers.c b/libguile/numbers.c
index afe5e55..a01549e 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -89,6 +89,11 @@ verify (FLT_RADIX == 2);
/* Make sure that scm_t_inum fits within a SCM value. */
verify (sizeof (scm_t_inum) <= sizeof (scm_t_bits));
+/* Several functions below assume that fixnums fit within a long, and
+ furthermore that there is some headroom to spare for other operations
+ without overflowing. */
+verify (SCM_I_FIXNUM_BIT <= SCM_LONG_BIT - 2);
+
#define scm_from_inum(x) (scm_from_signed_integer (x))
/* Test an inum to see if it can be converted to a double without loss
@@ -5125,12 +5130,11 @@ SCM_DEFINE (scm_round_ash, "round-ash", 2, 0, 0,
bits_to_shift = SCM_I_INUM (count);
else if (scm_is_signed_integer (count, LONG_MIN, LONG_MAX))
bits_to_shift = scm_to_long (count);
- else if (scm_is_false (scm_positive_p (scm_sum (scm_integer_length (n),
- count))))
- /* Huge right shift that eliminates all but the sign bit */
- return scm_is_false (scm_negative_p (n))
- ? SCM_INUM0 : SCM_I_MAKINUM (-1);
- else if (scm_is_true (scm_zero_p (n)))
+ else if (scm_is_true (scm_negative_p (scm_sum (scm_integer_length (n),
+ count)))
+ || scm_is_true (scm_zero_p (n)))
+ /* If N is zero, or the right shift count exceeds the integer
+ length, the result is zero. */
return SCM_INUM0;
else
scm_num_overflow ("round-ash");
diff --git a/test-suite/tests/numbers.test b/test-suite/tests/numbers.test
index 4e0bc82..8cecb06 100644
--- a/test-suite/tests/numbers.test
+++ b/test-suite/tests/numbers.test
@@ -5377,7 +5377,7 @@
;;;
(let ()
- (define (test-ash-variant name ash-variant round-variant)
+ (define (test-ash-variant name ash-variant round-variant rounded?)
(with-test-prefix name
(define (test n count)
(pass-if (list n count)
@@ -5434,17 +5434,17 @@
0
(ash-variant 123 (- (expt 2 1000))))
(pass-if-equal "Huge right shift of negative integer"
- -1
+ (if rounded? 0 -1)
(ash-variant -123 (- (expt 2 1000))))
(pass-if-equal "Huge right shift of -1"
- -1
+ (if rounded? 0 -1)
(ash-variant -1 (- (expt 2 1000))))
(pass-if-exception "Huge left shift of non-zero => numerical overflow"
exception:numerical-overflow
(ash-variant 123 (expt 2 1000)))))
- (test-ash-variant 'ash ash floor)
- (test-ash-variant 'round-ash round-ash round))
+ (test-ash-variant 'ash ash floor #f)
+ (test-ash-variant 'round-ash round-ash round #t))
;;;
;;; regressions