More comments on readwrite library; some refactoring ideas included.

[plomrogue] / src / readwrite.c

diff --git a/src/readwrite.c b/src/readwrite.c
index cdee90bbecbc62027aa7a5b55fe14b7ed4842a6d..e776ec2822636218908d237950ddb0939fa5bf2f 100644 (file)
--- a/src/readwrite.c
+++ b/src/readwrite.c
@@ -1,36 +1,115 @@
-/*  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 uint16_t, uint32_t */
+
+
+
+/* Read/write "x" from/to "file" as bigendian representation of "size" bits.
+ * Only multiples of 8 allowed for "size". On failure, return 1, else 0.
+ *
+ * As of of now, all other read/write functions build on top of these. TODO:
+ * Consider externing these so-far internal functions and dropping the
+ * interfaces to them, instead relying on their internal validity checks.
+ * (Usage of padded memory copies instead of directly manipulating * x as is
+ * done in read_uint* would need to be added, though.)
+ */
+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)
+{
+    if (0 != size % 8)           /* This bit number validity check is redundant */
+    {                            /* as long as this function is only available  */
+        return 1;                /* through extern interfaces pre-defining the  */
+    }                            /* bit number. TODO: Consider dropping it.     */
+    int16_t bitshift = size - 8;
+
+    * x = 0;
+    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)
+{
+    if (0 != size % 8)                             /* See comment             */
+    {                                              /* on identical            */
+        return 1;                                  /* code block in           */
+    }                                              /* read_uintX_bigendian(). */
+    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 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);
+}