bug#24908: Possible unboxing bug in master triggered by (format)

bug#24908: Possible unboxing bug in master triggered by (format)

[Daniel Llorens]

(format #f "~2f" 9.9) fails in master. You can try different combinations, it doesn't fail when it rounds down or there're more spaces for example.

The first bad commit is 0f2f5949a21572fad8355473200c7adc6d74f882 'Better unboxing' on the master branch.

See the full error below. 18446744073709551615 is 2^64-1 of course so it looks like bad signedness somewhere.

Regards

	Daniel


> guile -c '(use-modules (ice-9 format)) (format #f "~2f" 9.9)'
Backtrace:./meta/guile -c '(use-modules (ice-9 format)) (format #f "~2f" 9.9)'
Backtrace:
           8 (apply-smob/1 #<catch-closure 1105c20>)
In ice-9/boot-9.scm:
    704:2  7 (call-with-prompt ("prompt") #<procedure 110a060 at ic…> …)
In ice-9/eval.scm:
    608:8  6 (_ #(#(#<directory (guile-user) 110cf30>)))
In ice-9/command-line.scm:
   181:18  5 (_ #<input: string 1119f50>)
In unknown file:
           4 (eval (format #f "~2f" 9.9) #<directory (guile-user) 11…>)
In ice-9/format.scm:
  1590:19  3 (format #f "~2f" 9.9)
   316:19  2 (format:format-work "~2f" (9.9))
  1142:30  1 (format:out-fixed #f _ _)
  1525:37  0 (format:fn-round _)

ice-9/format.scm:1525:37: In procedure format:fn-round:
ice-9/format.scm:1525:37: In procedure string-ref: Value out of range: 18446744073709551615

bug#24908: workaround

[daniel.llorens]

I can't fix the compiler, so just patch format:fn-round. Includes a
test.

bug#24908: [PATCH] Workaround for bug #24908

[daniel.llorens]

From: Daniel Llorens <daniel.llorens@bluewin.ch>

* module/ice-9/format.scm (format:fn-round): Don't let i become
  negative.
* test-suite/tests/format.test: Regression test for "~2f".
---
 module/ice-9/format.scm      | 15 ++++++++-------
 test-suite/tests/format.test |  6 +++++-
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/module/ice-9/format.scm b/module/ice-9/format.scm
index 1ef4cb5ef..d3066a527 100644
--- a/module/ice-9/format.scm
+++ b/module/ice-9/format.scm
@@ -1510,11 +1510,12 @@
            (set! format:fn-len (- format:fn-len n)))
         (string-set! format:fn-str (- i n) (string-ref format:fn-str i))))
 
+    ;; carry i+1 to work around bug #24908
     (define (format:fn-round digits)    ; round format:fn-str
       (set! digits (+ digits format:fn-dot))
-      (do ((i digits (- i 1))		; "099",2 -> "10"
+      (do ((i (+ digits 1) (- i 1))	; "099",2 -> "10"
            (c 5))                       ; "023",2 -> "02"
-          ((or (= c 0) (< i 0))         ; "999",2 -> "100"
+          ((or (= c 0) (<= i 0))        ; "999",2 -> "100"
            (if (= c 1)			; "005",2 -> "01"
                (begin			; carry overflow
                  (set! format:fn-len digits)
@@ -1522,12 +1523,12 @@
                  (string-set! format:fn-str 0 #\1)
                  (set! format:fn-dot (+ format:fn-dot 1)))
                (set! format:fn-len digits)))
-        (set! c (+ (- (char->integer (string-ref format:fn-str i))
+        (set! c (+ (- (char->integer (string-ref format:fn-str (- i 1)))
                       format:zero-ch) c))
-        (string-set! format:fn-str i (integer->char
-                                      (if (< c 10) 
-                                          (+ c format:zero-ch)
-                                          (+ (- c 10) format:zero-ch))))
+        (string-set! format:fn-str (- i 1) (integer->char
+                                            (if (< c 10)
+                                              (+ c format:zero-ch)
+                                              (+ (- c 10) format:zero-ch))))
         (set! c (if (< c 10) 0 1))))
 
     (define (format:fn-out modifier add-leading-zero?)
diff --git a/test-suite/tests/format.test b/test-suite/tests/format.test
index cc31942cc..8aab7e96b 100644
--- a/test-suite/tests/format.test
+++ b/test-suite/tests/format.test
@@ -112,7 +112,11 @@
   ;; in guile prior to 1.6.9 and 1.8.1, leading zeros were incorrectly
   ;; stripped, moving the decimal point and giving "25.0" here
   (pass-if "string 02.5"
-    (string=? "2.5" (format #f "~f" "02.5"))))
+    (string=? "2.5" (format #f "~f" "02.5")))
+
+  ;; regression against bug #24908
+  (pass-if "2f"
+    (string=? "10." (format #f "~2f" 9.9))))
 
 ;;;
 ;;; ~h
-- 
2.11.0

bug#24908: closing

[Daniel Llorens]

Fixed in 2660c0b3c86bf76fab465c200a5ca20fb37cf811.