Fix signed int64 minimum formatting without overflow

engine/lib/libfmt.c

@@ -117,6 +117,7 @@ static sxi32 InternFormat(ProcConsumer xConsumer, void *pUserData, const char *z
 	sxu8 flag_zeropad;       /* True if field width constant starts with zero */
 	sxu8 flag_long;          /* True if "l" flag is present */
 	sxi64 longvalue;         /* Value for integer types */
+	sxu64 magnitude;         /* Unsigned magnitude for radix conversion */
 	const SyFmtInfo *infop;  /* Pointer to the appropriate info structure */
 	char buf[SXFMT_BUFSIZ];  /* Conversion buffer */
 	char prefix;             /* Prefix character."+" or "-" or " " or '\0'.*/
@@ -294,14 +295,11 @@ static sxi32 InternFormat(ProcConsumer xConsumer, void *pUserData, const char *z
 					flag_alternateform = 0;
 				}
 #endif
+				magnitude = (sxu64)longvalue;
 				if(infop->flags & SXFLAG_SIGNED) {
 					if(longvalue < 0) {
-						longvalue = -longvalue;
-						/* Ticket 1433-003 */
-						if(longvalue < 0) {
-							/* Overflow */
-							longvalue = SXI64_HIGH;
-						}
+						/* Unsigned subtraction also handles the signed minimum. */
+						magnitude = (sxu64)0 - magnitude;
 						prefix = '-';
 					} else if(flag_plussign) {
 						prefix = '+';
@@ -312,11 +310,10 @@ static sxi32 InternFormat(ProcConsumer xConsumer, void *pUserData, const char *z
 					}
 				} else {
 					if(longvalue < 0) {
-						longvalue = -longvalue;
-						/* Ticket 1433-003 */
-						if(longvalue < 0) {
-							/* Overflow */
-							longvalue = SXI64_HIGH;
+						magnitude = (sxu64)0 - magnitude;
+						/* Preserve the existing unsigned/radix overflow fallback. */
+						if(magnitude > (sxu64)SXI64_HIGH) {
+							magnitude = SXI64_HIGH;
 						}
 					}
 					prefix = 0;
@@ -331,9 +328,9 @@ static sxi32 InternFormat(ProcConsumer xConsumer, void *pUserData, const char *z
 					cset = infop->charset;
 					base = infop->base;
 					do {                                          /* Convert to ascii */
-						*(--bufpt) = cset[longvalue % base];
-						longvalue = longvalue / base;
-					} while(longvalue > 0);
+						*(--bufpt) = cset[magnitude % base];
+						magnitude = magnitude / base;
+					} while(magnitude > 0);
 				}
 				length = &buf[SXFMT_BUFSIZ - 1] - bufpt;
 				for(idx = precision - length; idx > 0; idx--) {