From: Chris Hanson <org/chris-hanson/cph>
Date: Sun, 29 Jan 2017 06:00:21 +0000 (-0800)
Subject: Fix bug: would-block value only returned if nothing has been read.
X-Git-Tag: mit-scheme-pucked-9.2.12~227^2~35
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=72ac4b3e49aeb49d4e7542ef27a3c5749a1516e7;p=mit-scheme.git

Fix bug: would-block value only returned if nothing has been read.
---

diff --git a/src/runtime/genio.scm b/src/runtime/genio.scm
index 8669b9b59..4f9e78fbc 100644
--- a/src/runtime/genio.scm
+++ b/src/runtime/genio.scm
@@ -236,8 +236,12 @@ USA.
   (let loop ((index start))
     (if (fix:< index end)
 	(let ((char (generic-io/read-char port)))
-	  (cond ((not char) #f)
-		((eof-object? char) (fix:- index start))
+	  (cond ((not char)
+		 (if (fix:< start index)
+		     (fix:- index start)
+		     #f))
+		((eof-object? char)
+		 (fix:- index start))
 		(else
 		 (ustring-set! string index char)
 		 (loop (fix:+ index 1)))))