fixed return values for ti_(Rewind/Tell/GetSize) and fixed ftell

Author: ZERICO2005

src/fileioc/fileioc.asm

@@ -827,8 +827,8 @@ ti_Rewind:
 	or	a, a
 	sbc	hl, hl
 	ret
-	scf
 .ret_neg_one:
+	scf
 	sbc	hl, hl
 	ret
 
@@ -850,6 +850,7 @@ ti_Tell:
 	pop	hl
 	ret
 .ret_neg_one:
+	scf
 	sbc	hl, hl
 	ret
 
@@ -871,6 +872,7 @@ ti_GetSize:
 	pop	hl
 	ret
 .ret_neg_one:
+	scf
 	sbc	hl, hl
 	ret
 

src/libc/ftell.c

@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <fileioc.h>
+#include <stdint.h>
 
 long int __attribute__((weak)) ftell(FILE *stream)
 {
@@ -11,5 +12,8 @@ long int __attribute__((weak)) ftell(FILE *stream)
         return -1L;
     }
 
-    return (long int)ti_Tell(stream->slot);
+    // ti_Tell shouldn't return a value greater than OS_VAR_MAX_SIZE (65512) unless an error occurs
+    uint16_t ret = ti_Tell(stream->slot);
+    // Convert a result of UINT16_MAX to -1L, leaving other results the same
+    return ((uint16_t)ret + 1) - 1L;
 }