Limit FatFs' ability to upper case paths

Only uppercase ASCII letters a-z. This saves ~900 bytes. Previously
written files with other unicode letters will only be accessible
from their upper cased path.

Author: tannewt

lib/oofatfs/ff.c

@@ -278,6 +278,12 @@ typedef struct {
 
 
 /* SBCS up-case tables (\x80-\xFF) */
+// Optimize the 437-only case with a truncated lookup table.
+#if FF_CODE_PAGE == 437
+#define TBL_CT437  {0x80,0x9A,0x45,0x41,0x8E,0x41,0x8F,0x80,0x45,0x45,0x45,0x49,0x49,0x49,0x8E,0x8F, \
+                    0x90,0x92,0x92,0x4F,0x99,0x4F,0x55,0x55,0x59,0x99,0x9A,0x9B,0x9C,0x9D,0x9E,0x9F, \
+                    0x41,0x49,0x4F,0x55,0xA5}
+#else
 #define TBL_CT437  {0x80,0x9A,0x45,0x41,0x8E,0x41,0x8F,0x80,0x45,0x45,0x45,0x49,0x49,0x49,0x8E,0x8F, \
                     0x90,0x92,0x92,0x4F,0x99,0x4F,0x55,0x55,0x59,0x99,0x9A,0x9B,0x9C,0x9D,0x9E,0x9F, \
                     0x41,0x49,0x4F,0x55,0xA5,0xA5,0xA6,0xA7,0xA8,0xA9,0xAA,0xAB,0xAC,0xAD,0xAE,0xAF, \
@@ -286,6 +292,7 @@ typedef struct {
                     0xD0,0xD1,0xD2,0xD3,0xD4,0xD5,0xD6,0xD7,0xD8,0xD9,0xDA,0xDB,0xDC,0xDD,0xDE,0xDF, \
                     0xE0,0xE1,0xE2,0xE3,0xE4,0xE5,0xE6,0xE7,0xE8,0xE9,0xEA,0xEB,0xEC,0xED,0xEE,0xEF, \
                     0xF0,0xF1,0xF2,0xF3,0xF4,0xF5,0xF6,0xF7,0xF8,0xF9,0xFA,0xFB,0xFC,0xFD,0xFE,0xFF}
+#endif
 #define TBL_CT720  {0x80,0x81,0x82,0x83,0x84,0x85,0x86,0x87,0x88,0x89,0x8A,0x8B,0x8C,0x8D,0x8E,0x8F, \
                     0x90,0x91,0x92,0x93,0x94,0x95,0x96,0x97,0x98,0x99,0x9A,0x9B,0x9C,0x9D,0x9E,0x9F, \
                     0xA0,0xA1,0xA2,0xA3,0xA4,0xA5,0xA6,0xA7,0xA8,0xA9,0xAA,0xAB,0xAC,0xAD,0xAE,0xAF, \
@@ -2887,7 +2894,12 @@ static FRESULT create_name (    /* FR_OK: successful, FR_INVALID_NAME: could not
             }
 #elif FF_CODE_PAGE < 900    /* SBCS cfg */
             wc = ff_uni2oem(wc, CODEPAGE);          /* Unicode ==> ANSI/OEM code */
+            // Optimize the 437-only case with a truncated lookup table.
+#if FF_CODE_PAGE == 437
+            if (wc & 0x80 && wc < (0xA5 - 0x80)) wc = ExCvt[wc & 0x7F];   /* Convert extended character to upper (SBCS) */
+#else
             if (wc & 0x80) wc = ExCvt[wc & 0x7F];   /* Convert extended character to upper (SBCS) */
+#endif
 #else                       /* DBCS cfg */
             wc = ff_uni2oem(ff_wtoupper(wc), CODEPAGE); /* Unicode ==> Upper convert ==> ANSI/OEM code */
 #endif

lib/oofatfs/ffunicode.c

@@ -499,6 +499,13 @@ DWORD ff_wtoupper ( /* Returns up-converted code point */
     DWORD uni       /* Unicode code point to be up-converted */
 )
 {
+    #if FF_FS_ASCII_UPPER_ONLY
+    // Only uppercase ASCII characters. Everything else will require the user to
+    // pass in an uppercase version.
+    if ('a' <= uni && uni <= 'z') {
+        uni -= 32;
+    }
+    #else
     const WORD *p;
     WORD uc, bc, nc, cmd;
     static const WORD cvt1[] = {    /* Compressed up conversion table for U+0000 - U+0FFF */
@@ -619,6 +626,7 @@ DWORD ff_wtoupper ( /* Returns up-converted code point */
         }
         uni = uc;
     }
+    #endif
 
     return uni;
 }

py/circuitpy_mpconfig.h

@@ -594,6 +594,8 @@ void supervisor_run_background_tasks_if_tick(void);
 #define CIRCUITPY_DIGITALIO_HAVE_INVALID_DRIVE_MODE (0)
 #endif
 
+#define FF_FS_ASCII_UPPER_ONLY (1)
+
 #define FF_FS_MAKE_VOLID (1)
 
 #define MICROPY_PY_OPTIMIZE_PROPERTY_FLASH_SIZE (CIRCUITPY_OPTIMIZE_PROPERTY_FLASH_SIZE)