More comments on readwrite library; some refactoring ideas included.

[plomrogue] / src / readwrite.c

diff --git a/src/readwrite.c b/src/readwrite.c
index 40fc63f0a5feb5c8f210e3c06a0060400cb80ab2..e776ec2822636218908d237950ddb0939fa5bf2f 100644 (file)
--- a/src/readwrite.c
+++ b/src/readwrite.c
@@ -6,40 +6,110 @@
 
 
 
-extern uint16_t read_uint16_bigendian(FILE * file)
+/* 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)
 {
-    uint16_t x;
-    x =     (uint16_t) fgetc(file) << 8;
-    x = x + (uint16_t) fgetc(file);
-    return x;
+    return read_uintX_bigendian(file, x, 32);
 }
 
 
 
-extern uint32_t read_uint32_bigendian(FILE * file)
+extern uint8_t write_uint8(uint8_t x, FILE * file)
 {
-    uint32_t x;
-    x =       (uint32_t) fgetc(file) << 24;
-    x = x + ( (uint32_t) fgetc(file) << 16 );
-    x = x + ( (uint32_t) fgetc(file) <<  8 );
-    x = x +   (uint32_t) fgetc(file);
-    return x;
+    return write_uintX_bigendian(file, x, 8);
 }
 
 
 
-extern void write_uint16_bigendian(uint16_t x, FILE * file)
+extern uint8_t write_uint16_bigendian(uint16_t x, FILE * file)
 {
-    fputc( x >> 8,   file );
-    fputc( x & 0xFF, file );
+    return write_uintX_bigendian(file, x, 16);
 }
 
 
 
-extern void write_uint32_bigendian(uint32_t x, FILE * file)
+extern uint8_t write_uint32_bigendian(uint32_t x, FILE * file)
 {
-    fputc(   x >> 24,          file);
-    fputc( ( x >> 16 ) & 0xFF, file);
-    fputc( ( x >>  8 ) & 0xFF, file);
-    fputc(   x         & 0xFF, file);
+    return write_uintX_bigendian(file, x, 32);
 }