This only breaks on platforms where 'char' is signed.

(currently, pmmx and x86_64)

--- free42/common/core_display.cc.old	2019-01-13 14:52:39.000000000 +0000
+++ free42/common/core_display.cc	2019-04-17 23:01:56.398695993 +0000
@@ -43,7 +43,7 @@
 #endif
 
 
-static char bigchars[130][5] =
+static unsigned char bigchars[130][5] =
     {
         { 0x08, 0x08, 0x2a, 0x08, 0x08 },
         { 0x22, 0x14, 0x08, 0x14, 0x22 },