summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
Diffstat
-rw-r--r--src/bitfield/bitfield.c185
-rw-r--r--src/bitfield/bitfield.h17
-rw-r--r--tests/bitfield_tests.c46
3 files changed, 219 insertions, 29 deletions
diff --git a/src/bitfield/bitfield.c b/src/bitfield/bitfield.c
index d383db04..b3aef4b2 100644
--- a/src/bitfield/bitfield.c
+++ b/src/bitfield/bitfield.c
@@ -1,47 +1,147 @@
#include <bitfield/bitfield.h>
+#include <limits.h>
+#include <string.h>
+#include <stddef.h>
+
+#define NIBBLE_SIZE (CHAR_BIT / 2)
+
+#define PREPARE_FIRST_COPY() \
+ do { \
+ if (source_length >= (CHAR_BIT - destination_offset_modulo)) { \
+ *destination &= reverse_mask[destination_offset_modulo]; \
+ source_length -= CHAR_BIT - destination_offset_modulo; \
+ } else { \
+ *destination &= reverse_mask[destination_offset_modulo] \
+ | reverse_mask_xor[destination_offset_modulo + source_length + 1];\
+ c &= reverse_mask[destination_offset_modulo + source_length ];\
+ source_length = 0; \
+ } } while (0)
/**
* Find the ending bit of a bitfield within the final byte.
*
* Returns: a bit position from 0 to 7.
*/
-int findEndBit(int startBit, int numBits) {
- int endBit = (startBit + numBits) % 8;
- return endBit == 0 ? 8 : endBit;
-}
-
-uint64_t bitmask(int numBits) {
- return (((uint64_t)0x1) << numBits) - 1;
+static uint8_t findEndBit(const uint16_t startBit, const uint16_t numBits) {
+ int endBit = (startBit + numBits) % CHAR_BIT;
+ return endBit == 0 ? CHAR_BIT : endBit;
}
-int startingByte(int startBit) {
- return startBit / 8;
-}
-int endingByte(int startBit, int numBits) {
- return (startBit + numBits - 1) / 8;
+// TODO can probably remove this
+static int byteForBit(const uint16_t startBit) {
+ return startBit / CHAR_BIT;
}
-uint64_t getBitField(uint64_t data, int startBit, int numBits, bool bigEndian) {
- int startByte = startingByte(startBit);
- int endByte = endingByte(startBit, numBits);
+/* Thanks to
+ * http://stackoverflow.com/questions/3534535/whats-a-time-efficient-algorithm-to-copy-unaligned-bit-arrays
+ */
+static void bitarray_copy(const uint8_t* source_origin, int source_offset,
+ int source_length, uint8_t* destination_origin, int destination_offset) {
+ static const uint8_t mask[] =
+ { 0x55, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff };
+ static const uint8_t reverse_mask[] =
+ { 0x55, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe, 0xff };
+ static const uint8_t reverse_mask_xor[] =
+ { 0xff, 0x7f, 0x3f, 0x1f, 0x0f, 0x07, 0x03, 0x01, 0x00 };
- if(!bigEndian) {
- data = __builtin_bswap64(data);
+ if(source_length < 1) {
+ return;
}
- uint8_t* bytes = (uint8_t*)&data;
- uint64_t ret = bytes[startByte];
- if(startByte != endByte) {
- // The lowest byte address contains the most significant bit.
- int i;
- for(i = startByte + 1; i <= endByte; i++) {
- ret = ret << 8;
- ret = ret | bytes[i];
+
+ int source_offset_modulo;
+ int destination_offset_modulo;
+
+ const uint8_t* source = source_origin + byteForBit(source_offset);
+ uint8_t* destination = destination_origin + byteForBit(destination_offset);
+
+ source_offset_modulo = source_offset % CHAR_BIT;
+ destination_offset_modulo = destination_offset % CHAR_BIT;
+
+ if(source_offset_modulo == destination_offset_modulo) {
+ if(source_offset_modulo) {
+ uint8_t c;
+
+ c = reverse_mask_xor[destination_offset_modulo] & *source++;
+
+ PREPARE_FIRST_COPY();
+ *destination++ |= c;
+ }
+
+ int byte_len = source_length / CHAR_BIT;
+ int source_length_modulo = source_length % CHAR_BIT;
+
+ if(byte_len) {
+ memcpy(destination, source, byte_len);
+ source += byte_len;
+ destination += byte_len;
+ }
+ if(source_length_modulo) {
+ *destination &= reverse_mask_xor[source_length_modulo];
+ *destination |= reverse_mask[source_length_modulo] & *source;
+ }
+ } else {
+ int bit_diff_ls;
+ int bit_diff_rs;
+ uint8_t c;
+ /*
+ * Begin: Line things up on destination.
+ */
+ if (source_offset_modulo > destination_offset_modulo) {
+ bit_diff_ls = source_offset_modulo - destination_offset_modulo;
+ bit_diff_rs = CHAR_BIT - bit_diff_ls;
+
+ c = *source++ << bit_diff_ls;
+ c |= *source >> bit_diff_rs;
+ c &= reverse_mask_xor[destination_offset_modulo];
+ } else {
+ bit_diff_rs = destination_offset_modulo - source_offset_modulo;
+ bit_diff_ls = CHAR_BIT - bit_diff_rs;
+
+ c = *source >> bit_diff_rs &
+ reverse_mask_xor[destination_offset_modulo];
+ }
+ PREPARE_FIRST_COPY();
+ *destination++ |= c;
+
+ /*
+ * Middle: copy with only shifting the source.
+ */
+ int byte_len = source_length / CHAR_BIT;
+
+ while(--byte_len >= 0) {
+ c = *source++ << bit_diff_ls;
+ c |= *source >> bit_diff_rs;
+ *destination++ = c;
+ }
+
+ /*
+ * End: copy the remaing bits;
+ */
+ int source_length_modulo = source_length % CHAR_BIT;
+ if(source_length_modulo) {
+ c = *source++ << bit_diff_ls;
+ c |= *source >> bit_diff_rs;
+ c &= reverse_mask[source_length_modulo];
+
+ *destination &= reverse_mask_xor[source_length_modulo];
+ *destination |= c;
}
}
+}
+
+uint64_t bitmask(const uint8_t numBits) {
+ return (((uint64_t)0x1) << numBits) - 1;
+}
- ret >>= 8 - findEndBit(startBit, numBits);
- return ret & bitmask(numBits);
+uint64_t getBitField(uint64_t data, const uint16_t startBit,
+ const uint16_t numBits, bool bigEndian) {
+ uint64_t result;
+ getBits(startBit, numBits, (const uint8_t*)&data,
+ CHAR_BIT * sizeof(uint64_t),
+ bigEndian ? ENDIANNESS_BIG_ENDIAN : ENDIANNESS_LITTLE_ENDIAN,
+ &result);
+ return result;
}
/**
@@ -56,5 +156,34 @@ void setBitField(uint64_t* data, uint64_t value, int startBit, int numBits) {
}
uint8_t nthByte(uint64_t source, int byteNum) {
- return (source >> (64 - ((byteNum + 1) * 8))) & 0xFF;
+ return (source >> (64 - ((byteNum + 1) * CHAR_BIT))) & 0xFF;
+}
+
+uint8_t getNibble(const uint8_t nibble_index, const uint8_t data[],
+ const uint8_t length, Endianness endianness) {
+ 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;
+ }
+ }
+ result &= bitmask(NIBBLE_SIZE);
+ return result;
+}
+
+// TODO getBytes, return status and store in output parameter
+uint8_t getByte(const uint8_t byte_index, const uint8_t data[],
+ const uint8_t length, Endianness endianness) {
+ if(byte_index < length) {
+ return data[byte_index];
+ }
+ return 0;
+}
+
+void getBits(const uint16_t start_index, const uint16_t field_size,
+ const uint8_t data[], const uint8_t length, Endianness endianness,
+ uint8_t* result) {
+ bitarray_copy(data, start_index, field_size, result, 0);
}
diff --git a/src/bitfield/bitfield.h b/src/bitfield/bitfield.h
index 7d9f3995..ce68b949 100644
--- a/src/bitfield/bitfield.h
+++ b/src/bitfield/bitfield.h
@@ -8,6 +8,21 @@
extern "C" {
#endif
+typedef enum {
+ ENDIANNESS_LITTLE_ENDIAN,
+ ENDIANNESS_BIG_ENDIAN
+} Endianness;
+
+uint8_t getNibble(const uint8_t nibble_index, const uint8_t data[],
+ const uint8_t length, Endianness endianness);
+
+uint8_t getByte(const uint8_t byte_index, const uint8_t data[],
+ const uint8_t length, Endianness endianness);
+
+void getBits(const uint16_t start_index, const uint16_t field_size,
+ const uint8_t data[], const uint8_t length, Endianness endianness,
+ uint8_t* result);
+
/* Public: Reads a subset of bits from a byte array.
*
* data - the bytes in question.
@@ -40,7 +55,7 @@ extern "C" {
*
* Returns the value of the requested bit field.
*/
-uint64_t getBitField(uint64_t data, int startPos, int numBits, bool bigEndian);
+uint64_t getBitField(uint64_t data, const uint16_t startPos, const uint16_t numBits, bool bigEndian);
/* Public: Set the bit field in the given data array to the new value.
*
diff --git a/tests/bitfield_tests.c b/tests/bitfield_tests.c
index d248989b..f321e5f2 100644
--- a/tests/bitfield_tests.c
+++ b/tests/bitfield_tests.c
@@ -190,6 +190,48 @@ START_TEST(test_nth_byte)
}
END_TEST
+START_TEST (test_get_byte)
+{
+ uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
+ uint8_t result = getByte(0, data, sizeof(data), ENDIANNESS_BIG_ENDIAN);
+ ck_assert_int_eq(result, 0x12);
+ result = getByte(3, data, sizeof(data), ENDIANNESS_BIG_ENDIAN);
+ ck_assert_int_eq(result, 0x78);
+}
+END_TEST
+
+START_TEST (test_get_nibble)
+{
+ uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
+ uint8_t result = getNibble(0, data, sizeof(data), ENDIANNESS_BIG_ENDIAN);
+ ck_assert_int_eq(result, 0x1);
+ result = getNibble(1, data, sizeof(data), ENDIANNESS_BIG_ENDIAN);
+ ck_assert_int_eq(result, 0x2);
+ result = getNibble(2, data, sizeof(data), ENDIANNESS_BIG_ENDIAN);
+ ck_assert_int_eq(result, 0x3);
+}
+END_TEST
+
+START_TEST (test_get_bits)
+{
+ uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
+ uint8_t result[4];
+ getBits(0, 16, data, 36, ENDIANNESS_BIG_ENDIAN, result);
+ ck_assert_int_eq(result[0], 0x12);
+ ck_assert_int_eq(result[1], 0x34);
+}
+END_TEST
+
+START_TEST (test_get_uneven_bits)
+{
+ uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
+ uint8_t result[4] = {0};
+ getBits(4, 12, data, 36, ENDIANNESS_BIG_ENDIAN, result);
+ ck_assert_int_eq(result[0], 0x2);
+ ck_assert_int_eq(result[1], 0x34);
+}
+END_TEST
+
Suite* bitfieldSuite(void) {
Suite* s = suite_create("bitfield");
TCase *tc_core = tcase_create("core");
@@ -207,6 +249,10 @@ Suite* bitfieldSuite(void) {
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_get_byte);
+ tcase_add_test(tc_core, test_get_nibble);
+ tcase_add_test(tc_core, test_get_bits);
+ tcase_add_test(tc_core, test_get_uneven_bits);
suite_add_tcase(s, tc_core);
return s;