Enable (and fix) sign comparison warnings

GNUmakefile

@@ -1,5 +1,5 @@
 CFLAGS?=-g -O2 -fstack-protector-strong -D_FORTIFY_SOURCE=2
-override CFLAGS:=-Wall -Wno-switch -Wextra $(CFLAGS)
+override CFLAGS:=-Wall -Werror -Wno-switch -Wextra $(CFLAGS)
 LDLIBS=-lrt
 
 OS := $(shell uname)

blaze822.c

@@ -152,14 +152,18 @@ skip_comment(char *s)
 // never writes more than dstmax to dst
 // returns how many bytes were appended
 static size_t
-safe_append(char *dst, size_t dstmax, char *strbeg, char *strend)
+safe_append(char *dst, size_t dstmax, char *postbeg, char *postend)
 {
 	size_t dstlen = strlen(dst);
-	if (dstmax - dstlen - 1 < strend - strbeg)
-		strend = strbeg + (dstmax - dstlen - 1);
-	memcpy(dst + dstlen, strbeg, strend - strbeg);
-	dst[dstlen + (strend - strbeg)] = 0;
-	return strend - strbeg;
+        size_t postlen = postend - postbeg;
+        if (postend - postbeg < 0)
+		return 0;
+
+	if (dstmax - dstlen - 1 < postlen)
+		postlen = dstmax - dstlen - 1;
+	memcpy(dst + dstlen, postbeg, postlen);
+	dst[dstlen + postlen] = 0;
+	return postlen;
 }
 
 static size_t

mmime.c

@@ -314,7 +314,7 @@ print_header(char *line) {
 		if (!highbit) {
 			if (e-s >= 998)
 				goto force_qp;
-			if (e-s >= 78 - linelen) {
+			if (linelen + e-s >= 78) {
 				// wrap in advance before long word
 				printf("\n");
 				linelen = 0;
@@ -336,7 +336,7 @@ force_qp:
 				s++;
 			if (linelen >= 78 - 13 - 4 ||
 			    (e-s < (78 - 13)/3 &&
-			     e-s >= (78 - linelen - 13)/3)) {
+			     e-s >= (int)(78 - linelen - 13)/3)) {
 				// wrap in advance
 				printf("\n");
 				linelen = 0;