From becedd5bd29dd1ea3c21426568e6412d6b9a404e Mon Sep 17 00:00:00 2001
From: Ron Yorston <rmy@pobox.com>
Date: Mon, 30 Dec 2024 08:27:31 +0000
Subject: win32: code shrink quote_arg()

Alter quote_arg() to perform a single pass over the string in the
case where no change is required.  Based on a proposal by @avih in
GitHub PR #317.

Saves 16 bytes.
---
 win32/process.c | 44 ++++++++++++++++++++------------------------
 1 file changed, 20 insertions(+), 24 deletions(-)

diff --git a/win32/process.c b/win32/process.c
index a70b9484e..e7c9ca187 100644
--- a/win32/process.c
+++ b/win32/process.c
@@ -109,38 +109,34 @@ parse_interpreter(const char *cmd, interp_t *interp)
 char * FAST_FUNC
 quote_arg(const char *arg)
 {
-	char *r = xmalloc(2 * strlen(arg) + 3);  // max-esc, enclosing DQ, \0
-	char *d = r;
-	int nbs = 0;  // n consecutive BS right before current char
+	char *d, *r = xmalloc(2 * strlen(arg) + 3);	// max-esc, quotes, \0
+	size_t nbs = 0; // consecutive backslashes before current char
+	int quoted = !*arg;
 
-	/* empty arguments and those containing tab/space must be quoted */
-	if (!*arg || strpbrk(arg, " \t")) {
-		*d++ = '"';
-	}
+	for (d = r; *arg; *d++ = *arg++) {
+		if (*arg == ' ' || *arg == '\t')
+			quoted = 1;
+
+		if (*arg == '\\' || *arg == '"')
+			*d++ = '\\';
+		else
+			d -= nbs; // undo nbs escapes, if any (not followed by DQ)
 
-	while (*arg) {
-		switch (*arg) {
-		case '\\':
+		if (*arg == '\\')
 			++nbs;
-			break;
-		case '"':  // double consecutive-BS, plus one to escape the DQ
-			for (++nbs; nbs; --nbs)
-				*d++ = '\\';
-			break;
-		default:  // reset count if followed by not-DQ
+		else
 			nbs = 0;
-		}
-		*d++ = *arg++;
 	}
 
-	if (*r == '"') {
-		while (nbs--)  // double consecutive-BS before the closing DQ
-			*d++ = '\\';
-		*d++ = '"';
+	if (quoted) {
+		memmove(r + 1, r, d++ - r);
+		*r = *d++ = '"';
+	} else {
+		d -= nbs;
 	}
-	*d++ = '\0';
 
-	return xrealloc(r, d - r);
+	*d = 0;
+	return r;
 }
 
 char * FAST_FUNC
-- 
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