From 68b1e58a4d60c4988e0b34292a271ea006956fc1 Mon Sep 17 00:00:00 2001
From: Eugene <tweels@gmail.com>
Date: Fri, 7 Jun 2024 23:34:04 +0300
Subject: [PATCH] Allow src and dest buffers to be overlapped in Q_strncpy()
 for QVM compatibility reasons

---
 code/qcommon/q_shared.c | 44 +++++++++++++++++++++++++++++++++++------
 code/qcommon/q_shared.h |  2 +-
 code/server/sv_game.c   |  2 +-
 3 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/code/qcommon/q_shared.c b/code/qcommon/q_shared.c
index a7c69bcc0..ee1975fbb 100644
--- a/code/qcommon/q_shared.c
+++ b/code/qcommon/q_shared.c
@@ -1309,24 +1309,56 @@ void Q_strncpyz( char *dest, const char *src, int destsize )
 /*
 =============
 Q_strncpy
+
+allows src and dest to be overlapped for QVM compatibility purposes
 =============
 */
-char *Q_strncpy( char *dest, const char *src, int destsize )
+char *Q_strncpy( char *dest, char *src, int destsize )
 {
-	char *start = dest;
+	char *s = src, *start = dest;
+	int src_len;
 
-	while ( destsize > 0 && (*dest++ = *src++) != '\0' ) {
-		--destsize;
+	while ( *s != '\0' )
+		++s;
+	src_len = (int)(s - src);
+	
+	if ( src_len > destsize ) {
+		src_len = destsize;
+	}
+	destsize -= src_len;
+
+	if ( dest > src && dest < src + src_len ) {
+		int i;
+#ifdef _DEBUG
+		Com_Printf( S_COLOR_YELLOW "Q_strncpy: overlapped (dest > src) buffers\n" );
+#endif
+		for ( i = src_len - 1; i >= 0; --i ) {
+			dest[i] = src[i]; // back overlapping
+		}
+		dest += src_len;
+	} else {
+#ifdef _DEBUG
+		if ( src >= dest && src < dest + src_len ) {
+			Com_Printf( S_COLOR_YELLOW "Q_strncpy: overlapped (src >= dst) buffers\n" );
+#ifdef _MSC_VER
+			// __debugbreak();
+#endif 
+		}
+#endif
+		while ( src_len > 0 ) {
+			*dest++ = *src++;
+			--src_len;
+		}
 	}
 
-	while ( --destsize > 0 ) {
+	while ( destsize > 0 ) {
 		*dest++ = '\0';
+		--destsize;
 	}
 
 	return start;
 }
 
-
 /*
 =============
 Q_stricmpn
diff --git a/code/qcommon/q_shared.h b/code/qcommon/q_shared.h
index cfa260062..c6d3ba1dc 100644
--- a/code/qcommon/q_shared.h
+++ b/code/qcommon/q_shared.h
@@ -842,7 +842,7 @@ void	Q_strcat( char *dest, int size, const char *src );
 int     Q_replace( const char *str1, const char *str2, char *src, int max_len );
 
 char	*Q_stradd( char *dst, const char *src );
-char	*Q_strncpy( char *dest, const char *src, int destsize );
+char	*Q_strncpy( char *dest, char *src, int destsize );
 
 // strlen that discounts Quake color sequences
 int Q_PrintStrlen( const char *string );
diff --git a/code/server/sv_game.c b/code/server/sv_game.c
index 290947126..95eff21c3 100644
--- a/code/server/sv_game.c
+++ b/code/server/sv_game.c
@@ -487,7 +487,7 @@ static intptr_t SV_GameSystemCalls( intptr_t *args ) {
 		return 0;
 	case G_GET_ENTITY_TOKEN:
 		{
-			const char *s = COM_Parse( &sv.entityParsePoint );
+			char *s = (char*)COM_Parse( &sv.entityParsePoint );
 			VM_CHECKBOUNDS( gvm, args[1], args[2] );
 			//Q_strncpyz( VMA(1), s, args[2] );
 			// we can't use our optimized Q_strncpyz() function