-/* readwrite.c */
+/* readwrite.c */
#include "readwrite.h"
-#include <stdio.h>
-#include <stdint.h>
-#include <limits.h>
-
-static const uint16_t uchar_s = UCHAR_MAX + 1;
-
-extern uint16_t read_uint16_bigendian(FILE * file) {
- unsigned char a = fgetc(file);
- unsigned char b = fgetc(file);
- return (a * uchar_s) + b; }
-
-extern uint32_t read_uint32_bigendian(FILE * file) {
- unsigned char a = fgetc(file);
- unsigned char b = fgetc(file);
- unsigned char c = fgetc(file);
- unsigned char d = fgetc(file);
- return (a * uchar_s * uchar_s * uchar_s) + (b * uchar_s * uchar_s) + (c * uchar_s) + d; }
-
-extern void write_uint16_bigendian(uint16_t x, FILE * file) {
- unsigned char a = x / uchar_s;
- unsigned char b = x % uchar_s;
- fputc(a, file);
- fputc(b, file); }
-
-extern void write_uint32_bigendian(uint32_t x, FILE * file) {
- unsigned char a = x / (uchar_s * uchar_s * uchar_s);
- unsigned char b = (x - (a * uchar_s * uchar_s * uchar_s)) / (uchar_s * uchar_s);
- unsigned char c = (x - ((a * uchar_s * uchar_s * uchar_s) + (b * uchar_s * uchar_s))) / uchar_s;
- unsigned char d = x % uchar_s;
- fputc(a, file);
- fputc(b, file);
- fputc(c, file);
- fputc(d, file); }
+#include <stdio.h> /* for FILE typedef*/
+#include <stdint.h> /* for uint8_t, uint16_t, uint32_t */
+
+
+
+/* Read/write "x" from/to "file" as bigendian representation of "size" bits. On
+ * failure, return 1, else 0. (As of of now, all extern read/write functions
+ * build on top of these.)
+ *
+ * Only use multiples of 8 greater or equal 32 for "size", so that storage
+ * inside uint32_t is possible. Originally a bit number check prefaced the code
+ * of both functions. It was removed as redundant due to all possible "size"
+ * values being hardcoded into the library (i.e. in all extern functions calling
+ * / wrapping around either function). If this ever changes, (re-)insert:
+ *
+ * if (0 == size || size > 32 || 0 != size % 8)
+ * {
+ * return 1;
+ * }
+ */
+static uint8_t read_uintX_bigendian(FILE * file, uint32_t * x, uint8_t size);
+static uint8_t write_uintX_bigendian(FILE * file, uint32_t x, uint8_t size);
+
+
+static uint8_t read_uintX_bigendian(FILE * file, uint32_t * x, uint8_t size)
+{
+ * x = 0;
+ int16_t bitshift = size - 8;
+ int test;
+ for (; bitshift >= 0; bitshift = bitshift - 8)
+ {
+ test = fgetc(file);
+ if (EOF == test)
+ {
+ return 1;
+ }
+ * x = * x + ((uint32_t) test << bitshift);
+ }
+ return 0;
+}
+
+
+
+static uint8_t write_uintX_bigendian(FILE * file, uint32_t x, uint8_t size)
+{
+ int16_t bitshift = size - 8;
+ for (; bitshift >= 0; bitshift = bitshift - 8)
+ {
+ if (EOF == fputc((x >> bitshift) & 0xFF, file))
+ {
+ return 1;
+ }
+ }
+ return 0;
+}
+
+
+
+extern uint8_t read_uint8(FILE * file, uint8_t * x)
+{
+ /* Since read_uintX_bigendian() works on -- and zeroes -- four bytes, direct
+ * work on values of fewer bytes would corrupt immediate neighbor values.
+ */
+ uint32_t y = * x;
+ uint8_t err = read_uintX_bigendian(file, &y, 8);
+ * x = (uint8_t) y;
+ return err;
+}
+
+
+
+extern uint8_t read_uint16_bigendian(FILE * file, uint16_t * x)
+{
+ /* See read_uint8() introductory code comment for rationale. */
+ uint32_t y = * x;
+ uint8_t err = read_uintX_bigendian(file, &y, 16);
+ * x = (uint16_t) y;
+ return err;
+}
+
+
+
+extern uint8_t read_uint32_bigendian(FILE * file, uint32_t * x)
+{
+ return read_uintX_bigendian(file, x, 32);
+}
+
+
+
+extern uint8_t write_uint8(uint8_t x, FILE * file)
+{
+ return write_uintX_bigendian(file, x, 8);
+}
+
+
+
+extern uint8_t write_uint16_bigendian(uint16_t x, FILE * file)
+{
+ return write_uintX_bigendian(file, x, 16);
+}
+
+
+
+extern uint8_t write_uint32_bigendian(uint32_t x, FILE * file)
+{
+ return write_uintX_bigendian(file, x, 32);
+}