Standardize argument ordering for bitfield functions.

3 files changed, 72 insertions, 21 deletions

diff --git a/src/bitfield/bitfield.c b/src/bitfield/bitfield.c
index b0396413..934d5a6a 100644
--- a/src/bitfield/bitfield.c
+++ b/src/bitfield/bitfield.c
@@ -55,24 +55,21 @@ uint8_t nthByte(const uint64_t source, const uint16_t byteNum) {
     return (source >> (64 - ((byteNum + 1) * CHAR_BIT))) & 0xFF;
 }
 
-uint8_t getNibble(const uint8_t nibble_index, const uint8_t data[],
-        const uint8_t length) {
+uint8_t getNibble(const uint8_t source[], const uint8_t source_length,
+                const uint8_t nibble_index) {
     uint8_t byte_index = nibble_index / 2;
-    uint8_t result;
-    if(byte_index < length) {
-        result = data[byte_index];
-        if(nibble_index % 2 == 0) {
-            result >>= NIBBLE_SIZE;
-        }
+    uint8_t result = getByte(source, source_length, byte_index);
+    if(nibble_index % 2 == 0) {
+        result >>= NIBBLE_SIZE;
     }
     result &= bitmask(NIBBLE_SIZE);
     return result;
 }
 
-uint8_t getByte(const uint8_t byte_index, const uint8_t data[],
-        const uint8_t length) {
-    if(byte_index < length) {
-        return data[byte_index];
+uint8_t getByte(const uint8_t source[], const uint8_t source_length,
+        const uint8_t byte_index) {
+    if(byte_index < source_length) {
+        return source[byte_index];
     }
     return 0;
 }
diff --git a/src/bitfield/bitfield.h b/src/bitfield/bitfield.h
index bf5c9b7d..45e3ba26 100644
--- a/src/bitfield/bitfield.h
+++ b/src/bitfield/bitfield.h
@@ -8,11 +8,28 @@
 extern "C" {
 #endif
 
-uint8_t getNibble(const uint8_t nibble_index, const uint8_t data[],
-        const uint8_t length);
+/* Public: Return a single nibble from the byte array, with range checking.
+ *
+ * source - the source byte array.
+ * source_length - the total length of the source array.
+ * nibble_index - the index of the nibble to retreive. The leftmost nibble is
+ *      index 0.
+ *
+ * Returns the retreived nibble, right aligned in a uint8_t.
+ */
+uint8_t getNibble(const uint8_t source[], const uint8_t source_length,
+                const uint8_t nibble_index);
 
-uint8_t getByte(const uint8_t byte_index, const uint8_t data[],
-        const uint8_t length);
+/* Public: Return a single byte from the byte array, with range checking.
+ *
+ * source - the source byte array.
+ * source_length - the total length of the source array.
+ * byte_index - the index of the byte to retreive. The leftmost byte is index 0.
+ *
+ * Returns the retreived byte.
+ */
+uint8_t getByte(const uint8_t source[], const uint8_t source_length,
+        const uint8_t byte_index);
 
 /* Public: Copy a range of bits from one bit array to another.
  *
@@ -23,6 +40,17 @@ uint8_t getByte(const uint8_t byte_index, const uint8_t data[],
  * A bit array with regards to this function always has the leftmost bit in byte
  * 0, i.e. bit index is the leftmost bit of byte 0. Endianness does not matter.
  *
+ * For example:
+ *
+ *      uint8_t source[4] = {0x11, 0x22, 0x33, 0x44};
+ *      uint8_t destination[4] = {0};
+ *      copyBits(source, sizeof(source), 8, 8, destination,
+ *              sizeof(destination), 0);
+ *      // destination[0] == 0x22
+ *      // destination[1] == 0x0
+ *      // destination[2] == 0x0
+ *      // destination[3] == 0x0
+ *
  * Thanks to
  * http://stackoverflow.com/questions/3534535/whats-a-time-efficient-algorithm-to-copy-unaligned-bit-arrays
  * for the implementation of the algorithm.
@@ -50,6 +78,32 @@ bool copyBits(const uint8_t* source_origin, const uint16_t source_length,
         uint8_t* destination_origin, const uint16_t destination_length,
         const uint16_t destination_offset);
 
+/* Public: Copy a range of bits from one array to another, right aligning the
+ * result.
+ *
+ * This is mostly useful if you want to cast the result to an integer type
+ * instead of a byte array.
+ *
+ * For example:
+ *
+ *      uint8_t source[4] = {0x11, 0x22, 0x33, 0x44};
+ *      uint8_t destination[4] = {0};
+ *      copyBitsRightAligned(source, sizeof(source), 8, 8, destination,
+ *              sizeof(destination));
+ *      // destination[0] == 0x0
+ *      // destination[1] == 0x0
+ *      // destination[2] == 0x0
+ *      // destination[3] == 0x22
+ *
+ *      int value = (int)destination;
+ *      // value == 0x22 == 32
+ *
+ * The arguments are the same as copyBits, but without the destination_offset
+ * option - that's set automatically to right align the result.
+ *
+ * Returns true if the copy was successful and false if the range exceeded the
+ * size of the source or destination, or if the range size negative or 0.
+ */
 bool copyBitsRightAligned(const uint8_t source[], const uint16_t source_length,
                 const uint16_t offset, const uint16_t bit_count,
                 uint8_t* destination, const uint16_t destination_length);
diff --git a/tests/bitfield_tests.c b/tests/bitfield_tests.c
index e2304ea0..00a28a36 100644
--- a/tests/bitfield_tests.c
+++ b/tests/bitfield_tests.c
@@ -193,9 +193,9 @@ END_TEST
 START_TEST (test_get_byte)
 {
     uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
-    uint8_t result = getByte(0, data, sizeof(data));
+    uint8_t result = getByte(data, sizeof(data), 0);
     ck_assert_int_eq(result, 0x12);
-    result = getByte(3, data, sizeof(data));
+    result = getByte(data, sizeof(data), 3);
     ck_assert_int_eq(result, 0x78);
 }
 END_TEST
@@ -203,11 +203,11 @@ END_TEST
 START_TEST (test_get_nibble)
 {
     uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
-    uint8_t result = getNibble(0, data, sizeof(data));
+    uint8_t result = getNibble(data, sizeof(data), 0);
     ck_assert_int_eq(result, 0x1);
-    result = getNibble(1, data, sizeof(data));
+    result = getNibble(data, sizeof(data), 1);
     ck_assert_int_eq(result, 0x2);
-    result = getNibble(2, data, sizeof(data));
+    result = getNibble(data, sizeof(data), 2);
     ck_assert_int_eq(result, 0x3);
 }
 END_TEST