Subject: bug#14864: bitwise-arithmetic-shift-right is wrong for large shift amounts

From: Göran Weinholt <[email-masked]>
Date: Sun, 14 Jul 2013 18:08:55 +0200

Hello schemers,

bitwise-arithmetic-shift-right from (rnrs) is wrong for ridiculously
large shift amounts:

scheme@(guile-user)> (import (rnrs))
scheme@(guile-user)> (bitwise-arithmetic-shift-right -2 (+ (greatest-fixnum) 1))
$1 = -2

The correct result is -1. Tested on an amd64 system with
guile-2.0.9.20-10454-dirty. Here are a few more failing cases, if it
helps:

(bitwise-arithmetic-shift-right
  -1939573486025768832
  1842615318141600354)
=>
-112898036
; *** failed ***
; expected result: -1

(bitwise-arithmetic-shift-right
  1344211617424411880
  1877595747324902264)
=>
18
; *** failed ***
; expected result: 0

(bitwise-arithmetic-shift-right
  -1152921504606846979
  88553614889043251)
=>
-513
; *** failed ***
; expected result: -1

(bitwise-arithmetic-shift-right
  -870600743868926059
  1508151148)
=>
-49488
; *** failed ***
; expected result: -1

Regards,

-- 
Göran Weinholt <[email-masked]>
13             MR. JAKES:  I think our economy was based on
14 industrial process.
15             JUSTICE SCALIA:  It was based on horses, for
16 Pete's sake.