From 5183ddf2ed56519b669320095ed00528a71a9393 Mon Sep 17 00:00:00 2001
From: Jilles Tjoelker <jilles@FreeBSD.org>
Date: Tue, 16 May 2017 21:54:51 +0000
Subject: [PATCH] sh: Simplify output buffering.

Similarly to how STPUTC was changed, change struct output to store the
pointer just past the end of the available space instead of the size of the
available space, so after writing a character it is only necessary to
increment a pointer and not to decrement a counter.
---
 bin/sh/eval.c   |  7 +++++--
 bin/sh/output.c | 17 ++++++++---------
 bin/sh/output.h |  4 ++--
 3 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/bin/sh/eval.c b/bin/sh/eval.c
index e09549295f66..f637cfab5fd9 100644
--- a/bin/sh/eval.c
+++ b/bin/sh/eval.c
@@ -1080,8 +1080,8 @@ evalcommand(union node *cmd, int flags, struct backcmd *backcmd)
 #endif
 		mode = (cmdentry.u.index == EXECCMD)? 0 : REDIR_PUSH;
 		if (flags == EV_BACKCMD) {
-			memout.nleft = 0;
 			memout.nextc = memout.buf;
+			memout.bufend = memout.buf;
 			memout.bufsize = 64;
 			mode |= REDIR_BACKQ;
 		}
@@ -1134,8 +1134,11 @@ evalcommand(union node *cmd, int flags, struct backcmd *backcmd)
 			exitshell(exitstatus);
 		if (flags == EV_BACKCMD) {
 			backcmd->buf = memout.buf;
-			backcmd->nleft = memout.nextc - memout.buf;
+			backcmd->nleft = memout.buf != NULL ?
+			    memout.nextc - memout.buf : 0;
 			memout.buf = NULL;
+			memout.nextc = NULL;
+			memout.bufend = NULL;
 		}
 		if (cmdentry.u.index != EXECCMD)
 			popredir();
diff --git a/bin/sh/output.c b/bin/sh/output.c
index 2f9fc925d88c..64d311f0c2d6 100644
--- a/bin/sh/output.c
+++ b/bin/sh/output.c
@@ -71,9 +71,9 @@ __FBSDID("$FreeBSD$");
 
 static int doformat_wr(void *, const char *, int);
 
-struct output output = {NULL, 0, NULL, OUTBUFSIZ, 1, 0};
-struct output errout = {NULL, 0, NULL, 256, 2, 0};
-struct output memout = {NULL, 0, NULL, 0, MEM_OUT, 0};
+struct output output = {NULL, NULL, NULL, OUTBUFSIZ, 1, 0};
+struct output errout = {NULL, NULL, NULL, 256, 2, 0};
+struct output memout = {NULL, NULL, NULL, 0, MEM_OUT, 0};
 struct output *out1 = &output;
 struct output *out2 = &errout;
 
@@ -214,20 +214,19 @@ emptyoutbuf(struct output *dest)
 		INTOFF;
 		dest->buf = ckmalloc(dest->bufsize);
 		dest->nextc = dest->buf;
-		dest->nleft = dest->bufsize;
+		dest->bufend = dest->buf + dest->bufsize;
 		INTON;
 	} else if (dest->fd == MEM_OUT) {
-		offset = dest->bufsize;
+		offset = dest->nextc - dest->buf;
 		INTOFF;
 		dest->bufsize <<= 1;
 		dest->buf = ckrealloc(dest->buf, dest->bufsize);
-		dest->nleft = dest->bufsize - offset;
+		dest->bufend = dest->buf + dest->bufsize;
 		dest->nextc = dest->buf + offset;
 		INTON;
 	} else {
 		flushout(dest);
 	}
-	dest->nleft--;
 }
 
 
@@ -248,7 +247,6 @@ flushout(struct output *dest)
 	if (xwrite(dest->fd, dest->buf, dest->nextc - dest->buf) < 0)
 		dest->flags |= OUTPUT_ERR;
 	dest->nextc = dest->buf;
-	dest->nleft = dest->bufsize;
 }
 
 
@@ -258,8 +256,9 @@ freestdout(void)
 	INTOFF;
 	if (output.buf) {
 		ckfree(output.buf);
+		output.nextc = NULL;
 		output.buf = NULL;
-		output.nleft = 0;
+		output.bufend = NULL;
 	}
 	INTON;
 }
diff --git a/bin/sh/output.h b/bin/sh/output.h
index 21cbba1efa58..f43a60cc2aaa 100644
--- a/bin/sh/output.h
+++ b/bin/sh/output.h
@@ -40,7 +40,7 @@
 
 struct output {
 	char *nextc;
-	int nleft;
+	char *bufend;
 	char *buf;
 	int bufsize;
 	short fd;
@@ -75,7 +75,7 @@ void fmtstr(char *, int, const char *, ...) __printflike(3, 4);
 void doformat(struct output *, const char *, va_list) __printflike(2, 0);
 int xwrite(int, const char *, int);
 
-#define outc(c, file)	(--(file)->nleft < 0? (emptyoutbuf(file), *(file)->nextc++ = (c)) : (*(file)->nextc++ = (c)))
+#define outc(c, file)	((file)->nextc == (file)->bufend ? (emptyoutbuf(file), *(file)->nextc++ = (c)) : (*(file)->nextc++ = (c)))
 #define out1c(c)	outc(c, out1);
 #define out2c(c)	outcslow(c, out2);