Add get_byte and get_nibble to 8byte function set.

6 files changed, 91 insertions, 20 deletions

diff --git a/README.mkd b/README.mkd
index 836b151e..0ec51263 100644
--- a/README.mkd
+++ b/README.mkd
@@ -12,8 +12,13 @@ started, here are examples using the API:
 
     uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
     uint8_t result = get_byte(data, sizeof(data), 0);
-    uint8_t result = get_nibble(data, sizeof(data), 0);
-    fail_unless(copy_bits_right_aligned(data, 4, 4, 12, result, 4));
+    // result = 0x12;
+    result = get_nibble(data, sizeof(data), 0);
+    // result = 0x1;
+    bool success = copy_bits_right_aligned(data, 4, 4, 12, result, 4)
+    // success == true
+    // result[0] == 0x2
+    // result[1] == 0x34
 
 ## 8 Byte Bitfield Decoding
 
@@ -26,12 +31,15 @@ started, here are examples using the API:
     // result = 0x574d555a;
 
     data = 0x00000000F34DFCFF;
-    result = nth_byte(data, 0);
+    result = eightbyte_get_byte(data, 0, false);
     //result = 0x0
 
-    result = nth_byte(data, 4);
+    result = eightbyte_get_byte(data, 4, false);
     //result = 0xF3
 
+    result = eightbyte_get_nibble(data, 10, false);
+    //result = 0x4;
+
 ## 8 Byte Bitfield Encoding
 
     uint64_t data = 0;
diff --git a/src/bitfield/8byte.c b/src/bitfield/8byte.c
index 845be8c0..f08f227d 100644
--- a/src/bitfield/8byte.c
+++ b/src/bitfield/8byte.c
@@ -18,8 +18,21 @@ static uint16_t bits_to_bytes(uint32_t bits) {
     return byte_count;
 }
 
+uint8_t eightbyte_get_nibble(const uint64_t source, const uint8_t nibble_index,
+        const bool big_endian) {
+    return get_bit_field(source, NIBBLE_SIZE * nibble_index, NIBBLE_SIZE,
+            big_endian);
+}
+
+uint8_t eightbyte_get_byte(const uint64_t source, const uint8_t byte_index,
+        const bool big_endian) {
+    // TODO we're not handling swapped endianness - we could use get_bit_field
+    // but this might be more efficient
+    return (source >> (EIGHTBYTE_BIT - ((byte_index + 1) * CHAR_BIT))) & 0xFF;
+}
+
 uint64_t get_bit_field(uint64_t source, const uint16_t offset,
-        const uint16_t bit_count, bool big_endian) {
+        const uint16_t bit_count, const bool big_endian) {
     int startByte = offset / CHAR_BIT;
     int endByte = (offset + bit_count - 1) / CHAR_BIT;
 
@@ -54,8 +67,3 @@ bool set_bit_field(uint64_t* destination, uint64_t value, const uint16_t offset,
     *destination |= value;
     return true;
 }
-
-uint8_t nth_byte(const uint64_t source, const uint16_t byte_index) {
-    return (source >> (EIGHTBYTE_BIT - ((byte_index + 1) * CHAR_BIT))) & 0xFF;
-}
-
diff --git a/src/bitfield/8byte.h b/src/bitfield/8byte.h
index 1ee9c0ec..818372d5 100644
--- a/src/bitfield/8byte.h
+++ b/src/bitfield/8byte.h
@@ -47,7 +47,32 @@ extern "C" {
  * Returns the value of the requested bit field, right aligned in a uint64_t.
  */
 uint64_t get_bit_field(uint64_t source, const uint16_t offset,
-        const uint16_t bit_count, bool big_endian);
+        const uint16_t bit_count, const bool big_endian);
+
+/* Public: Return a single nibble from the payload, with range checking.
+ *
+ * source - the source payload.
+ * nibble_index - the index of the nibble to retreive. The leftmost nibble is
+ *      index 0.
+ * big_endian - if the data passed in is little endian, set this to false and it
+ *      will be flipped before grabbing the bit field.
+ *
+ * Returns the retreived nibble, right aligned in a uint8_t.
+ */
+uint8_t eightbyte_get_nibble(const uint64_t source, const uint8_t nibble_index,
+                const bool big_endian);
+
+/* Public: Return a single byte from the payload, with range checking.
+ *
+ * source - the source byte array.
+ * byte_index - the index of the byte to retreive. The leftmost byte is index 0.
+ * big_endian - if the data passed in is little endian, set this to false and it
+ *      will be flipped before grabbing the bit field.
+ *
+ * Returns the retreived byte.
+ */
+uint8_t eightbyte_get_byte(const uint64_t source, const uint8_t byte_index,
+                const bool big_endian);
 
 /* Public: Set the bit field in the given data array to the new value.
  *
diff --git a/src/bitfield/bitfield.c b/src/bitfield/bitfield.c
index 7dfa7cd4..af17d485 100644
--- a/src/bitfield/bitfield.c
+++ b/src/bitfield/bitfield.c
@@ -3,8 +3,6 @@
 #include <string.h>
 #include <stddef.h>
 
-#define NIBBLE_SIZE (CHAR_BIT / 2)
-
 uint8_t get_nibble(const uint8_t source[], const uint8_t source_length,
                 const uint8_t nibble_index) {
     uint8_t byte_index = nibble_index / 2;
diff --git a/src/bitfield/bitfield.h b/src/bitfield/bitfield.h
index 52ed143d..b58e4e59 100644
--- a/src/bitfield/bitfield.h
+++ b/src/bitfield/bitfield.h
@@ -4,6 +4,8 @@
 #include <stdint.h>
 #include <stdbool.h>
 
+#define NIBBLE_SIZE (CHAR_BIT / 2)
+
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/tests/8byte_tests.c b/tests/8byte_tests.c
index 6166f1d7..572253ce 100644
--- a/tests/8byte_tests.c
+++ b/tests/8byte_tests.c
@@ -172,31 +172,60 @@ START_TEST (test_set_odd_number_of_bits)
 }
 END_TEST
 
-START_TEST(test_nth_byte)
+START_TEST(test_eightbyte_get_byte)
 {
     uint64_t data = 0x00000000F34DFCFF;
-    uint8_t result = nth_byte(data, 0);
+    uint8_t result = eightbyte_get_byte(data, 0, false);
     uint8_t expected = 0x0;
     ck_assert_int_eq(result, expected);
 
-    result = nth_byte(data, 4);
+    result = eightbyte_get_byte(data, 4, false);
     expected = 0xF3;
     ck_assert_int_eq(result, expected);
 
-    result = nth_byte(data, 5);
+    result = eightbyte_get_byte(data, 5, false);
     expected = 0x4D;
     ck_assert_int_eq(result, expected);
 
-    result = nth_byte(data, 6);
+    result = eightbyte_get_byte(data, 6, false);
     expected = 0xFC;
     ck_assert_int_eq(result, expected);
 
-    result = nth_byte(data, 7);
+    result = eightbyte_get_byte(data, 7, false);
     expected = 0xFF;
     ck_assert_int_eq(result, expected);
 }
 END_TEST
 
+START_TEST(test_eightbyte_get_nibble)
+{
+    uint64_t data = 0x00000000F34DFCFF;
+    uint8_t result = eightbyte_get_nibble(data, 0, false);
+    uint8_t expected = 0x0;
+    ck_assert_int_eq(result, expected);
+
+    result = eightbyte_get_nibble(data, 2, false);
+    expected = 0x0;
+    ck_assert_int_eq(result, expected);
+
+    result = eightbyte_get_nibble(data, 8, false);
+    expected = 0xF;
+    ck_assert_int_eq(result, expected);
+
+    result = eightbyte_get_nibble(data, 9, false);
+    expected = 0x3;
+    ck_assert_int_eq(result, expected);
+
+    result = eightbyte_get_nibble(data, 10, false);
+    expected = 0x4;
+    ck_assert_int_eq(result, expected);
+
+    result = eightbyte_get_nibble(data, 13, false);
+    expected = 0xC;
+    ck_assert_int_eq(result, expected);
+}
+END_TEST
+
 Suite* bitfieldSuite(void) {
     Suite* s = suite_create("bitfield");
     TCase *tc_core = tcase_create("core");
@@ -214,7 +243,8 @@ Suite* bitfieldSuite(void) {
     tcase_add_test(tc_core, test_set_doesnt_clobber_existing_data);
     tcase_add_test(tc_core, test_set_off_byte_boundary);
     tcase_add_test(tc_core, test_set_odd_number_of_bits);
-    tcase_add_test(tc_core, test_nth_byte);
+    tcase_add_test(tc_core, test_eightbyte_get_nibble);
+    tcase_add_test(tc_core, test_eightbyte_get_byte);
     suite_add_tcase(s, tc_core);
 
     return s;