From: Chris Hanson <org/chris-hanson/cph>
Date: Tue, 26 May 1987 13:24:56 +0000 (+0000)
Subject: Add error check for positive arguments to signed integer coercion.
X-Git-Tag: 20090517-FFI~13482
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=64a1c2879d035e4d6a6ca202c41650d96e56b3a9;p=mit-scheme.git

Add error check for positive arguments to signed integer coercion.
---

diff --git a/v7/src/compiler/back/syntax.scm b/v7/src/compiler/back/syntax.scm
index b848e7cc0..d5c1d4da0 100644
--- a/v7/src/compiler/back/syntax.scm
+++ b/v7/src/compiler/back/syntax.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/back/syntax.scm,v 1.13 1987/03/19 00:50:43 cph Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/back/syntax.scm,v 1.14 1987/05/26 13:24:04 cph Exp $
 
 Copyright (c) 1987 Massachusetts Institute of Technology
 
@@ -186,12 +186,14 @@ MIT in each case. |#
   (unsigned-integer->bit-string nbits n))
 
 (define (coerce-signed-integer nbits)
-  (let ((offset (expt 2 nbits)))
+  (let* ((limit (expt 2 (-1+ nbits)))
+	 (offset (+ limit limit)))
     (lambda (n)
-      (unsigned-integer->bit-string nbits
-				    (if (negative? n)
-					(+ n offset)
-					n)))))
+      (unsigned-integer->bit-string
+       nbits
+       (cond ((negative? n) (+ n offset))
+	     ((< n limit) n)
+	     (else (error "Integer too large to be encoded" n)))))))
 
 (define (standard-coercion kernel)
   (lambda (nbits)
diff --git a/v7/src/runtime/bitstr.scm b/v7/src/runtime/bitstr.scm
index 42d49cec2..681e43c96 100644
--- a/v7/src/runtime/bitstr.scm
+++ b/v7/src/runtime/bitstr.scm
@@ -1,6 +1,6 @@
 ;;; -*-Scheme-*-
 ;;;
-;;;	$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/bitstr.scm,v 13.42 1987/04/25 20:18:51 cph Exp $
+;;;	$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/bitstr.scm,v 13.43 1987/05/26 13:24:56 cph Rel $
 ;;;
 ;;;	Copyright (c) 1987 Massachusetts Institute of Technology
 ;;;
@@ -73,10 +73,11 @@
     result))
 
 (define (signed-integer->bit-string nbits number)
-  (unsigned-integer->bit-string nbits
-				(if (negative? number)
-				    (+ number (expt 2 nbits))
-				    number)))
+  (unsigned-integer->bit-string
+   nbits
+   (cond ((negative? number) (+ number (expt 2 nbits)))
+	 ((< number (expt 2 (-1+ nbits))) number)
+	 (else (error "Integer too large to be encoded" number)))))
 
 (define (bit-string->signed-integer bit-string)
   (let ((unsigned-result (bit-string->unsigned-integer bit-string))