Split up 8 byte wrappers from generic bit array functions.

4 files changed, 130 insertions, 109 deletions

diff --git a/src/bitfield/8byte.c b/src/bitfield/8byte.c
new file mode 100644
index 00000000..0f249d93
--- /dev/null
+++ b/src/bitfield/8byte.c
@@ -0,0 +1,56 @@
+#include <bitfield/bitfield.h>
+#include <bitfield/8byte.h>
+#include <stddef.h>
+#include <limits.h>
+#include <string.h>
+
+uint64_t bitmask(const uint8_t numBits) {
+    return (((uint64_t)0x1) << numBits) - 1;
+}
+
+static uint16_t bitsToBytes(uint32_t bits) {
+    uint8_t byte_count = bits / CHAR_BIT;
+    if(bits % CHAR_BIT != 0) {
+        ++byte_count;
+    }
+    return byte_count;
+}
+
+uint64_t getBitField(uint64_t data, const uint16_t startBit,
+        const uint16_t numBits, bool bigEndian) {
+    uint8_t result[8] = {0};
+    if(!bigEndian) {
+        data = __builtin_bswap64(data);
+    }
+    copyBitsRightAligned((const uint8_t*)&data, sizeof(data), startBit, numBits,
+            result, sizeof(result));
+    uint64_t int_result = 0;
+
+    if(!bigEndian) {
+        // we need to swap the byte order of the array to get it into a
+        // uint64_t, but it's been right aligned so we have to be more careful
+        for(int i = 0; i < bitsToBytes(numBits); i++) {
+            int_result |= result[bitsToBytes(numBits) - i - 1] << (CHAR_BIT * i);
+        }
+    } else {
+        int_result = *(uint64_t*)result;
+    }
+    return int_result;
+}
+
+/**
+ * TODO it would be nice to have a warning if you call with this a value that
+ * won't fit in the number of bits you've specified it should use.
+ */
+void setBitField(uint64_t* data, uint64_t value, const uint16_t startPos,
+        const uint16_t numBits) {
+    int shiftDistance = 64 - startPos - numBits;
+    value <<= shiftDistance;
+    *data &= ~(bitmask(numBits) << shiftDistance);
+    *data |= value;
+}
+
+uint8_t nthByte(const uint64_t source, const uint16_t byteNum) {
+    return (source >> (64 - ((byteNum + 1) * CHAR_BIT))) & 0xFF;
+}
+
diff --git a/src/bitfield/8byte.h b/src/bitfield/8byte.h
new file mode 100644
index 00000000..13b6aff3
--- /dev/null
+++ b/src/bitfield/8byte.h
@@ -0,0 +1,74 @@
+#ifndef __8BYTE_H__
+#define __8BYTE_H__
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// TODO using uint64_t everywhere for CAN message payload is kind of cute, but
+// in actuality a CAN message may have a smaller payload, and it makes all of
+// these functions not applicable to other data sizes. It's also fairly
+// inefficient on 32-bit platforms. how much work is it to switch vi-firmware
+// to using uint8_t*?
+
+/* Public: Reads a subset of bits from a byte array.
+ *
+ * data - the bytes in question.
+ * startPos - the starting index of the bit field (beginning from 0).
+ * numBits - the width of the bit field to extract.
+ * bigEndian - if the data passed in is little endian, set this to false and it
+ *      will be flipped before grabbing the bit field.
+ *
+ * Bit fields are positioned according to big-endian bit layout, but inside the
+ * bit field, values are represented as little-endian. Therefore, to get the bit
+ * field, we swap the overall byte order if bigEndian == false and
+ * use the value we find in the field (assuming the embedded platform is little
+ * endian).
+ *
+ * For example, the bit layout of the value "42" (i.e. 00101010 set at position
+ * 14 with length 6 is:
+ *
+ *     000000000000001010100000000000000000000000000000000000000000000
+ *
+ * and the same value and position but with length 8 is:
+ *
+ *     000000000000000010101000000000000000000000000000000000000000000
+ *
+ * If the architecture where is code is running is little-endian, the input data
+ * will be swapped before grabbing the bit field.
+ *
+ * Examples
+ *
+ *  uint64_t value = getBitField(data, 2, 4);
+ *
+ * Returns the value of the requested bit field.
+ */
+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.
+ *
+ * data - a byte array with size at least startPos + numBits.
+ * value - the value to set in the bit field.
+ * startPos - the starting index of the bit field (beginning from 0).
+ */
+void setBitField(uint64_t* data, uint64_t value, const uint16_t startPos,
+        const uint16_t numBits);
+
+/* Public: Retreive the nth byte out of 8 bytes in a uint64_t.
+ *
+ * source - the source data to retreive the byte from.
+ * byteNum - the index of the byte, starting at 0 and assuming big-endian order.
+ *
+ * Returns the requested byte from the source bytes.
+ */
+uint8_t nthByte(const uint64_t source, const uint16_t byteNum);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // __8BYTE_H__
diff --git a/src/bitfield/bitfield.c b/src/bitfield/bitfield.c
index 934d5a6a..3bf00ac0 100644
--- a/src/bitfield/bitfield.c
+++ b/src/bitfield/bitfield.c
@@ -5,56 +5,6 @@
 
 #define NIBBLE_SIZE (CHAR_BIT / 2)
 
-uint64_t bitmask(const uint8_t numBits) {
-    return (((uint64_t)0x1) << numBits) - 1;
-}
-
-static uint16_t bitsToBytes(uint32_t bits) {
-    uint8_t byte_count = bits / CHAR_BIT;
-    if(bits % CHAR_BIT != 0) {
-        ++byte_count;
-    }
-    return byte_count;
-}
-
-uint64_t getBitField(uint64_t data, const uint16_t startBit,
-        const uint16_t numBits, bool bigEndian) {
-    uint8_t result[8] = {0};
-    if(!bigEndian) {
-        data = __builtin_bswap64(data);
-    }
-    copyBitsRightAligned((const uint8_t*)&data, sizeof(data), startBit, numBits,
-            result, sizeof(result));
-    uint64_t int_result = 0;
-
-    if(!bigEndian) {
-        // we need to swap the byte order of the array to get it into a
-        // uint64_t, but it's been right aligned so we have to be more careful
-        for(int i = 0; i < bitsToBytes(numBits); i++) {
-            int_result |= result[bitsToBytes(numBits) - i - 1] << (CHAR_BIT * i);
-        }
-    } else {
-        int_result = *(uint64_t*)result;
-    }
-    return int_result;
-}
-
-/**
- * TODO it would be nice to have a warning if you call with this a value that
- * won't fit in the number of bits you've specified it should use.
- */
-void setBitField(uint64_t* data, uint64_t value, const uint16_t startPos,
-        const uint16_t numBits) {
-    int shiftDistance = 64 - startPos - numBits;
-    value <<= shiftDistance;
-    *data &= ~(bitmask(numBits) << shiftDistance);
-    *data |= value;
-}
-
-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 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 45e3ba26..6f5f1c18 100644
--- a/src/bitfield/bitfield.h
+++ b/src/bitfield/bitfield.h
@@ -108,65 +108,6 @@ 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);
 
-// TODO using uint64_t everywhere for CAN message payload is kind of cute, but
-// in actuality a CAN message may have a smaller payload, and it makes all of
-// these functions not applicable to other data sizes. It's also fairly
-// inefficient on 32-bit platforms. how much work is it to switch vi-firmware
-// to using uint8_t*?
-
-/* Public: Reads a subset of bits from a byte array.
- *
- * data - the bytes in question.
- * startPos - the starting index of the bit field (beginning from 0).
- * numBits - the width of the bit field to extract.
- * bigEndian - if the data passed in is little endian, set this to false and it
- *      will be flipped before grabbing the bit field.
- *
- * Bit fields are positioned according to big-endian bit layout, but inside the
- * bit field, values are represented as little-endian. Therefore, to get the bit
- * field, we swap the overall byte order if bigEndian == false and
- * use the value we find in the field (assuming the embedded platform is little
- * endian).
- *
- * For example, the bit layout of the value "42" (i.e. 00101010 set at position
- * 14 with length 6 is:
- *
- *     000000000000001010100000000000000000000000000000000000000000000
- *
- * and the same value and position but with length 8 is:
- *
- *     000000000000000010101000000000000000000000000000000000000000000
- *
- * If the architecture where is code is running is little-endian, the input data
- * will be swapped before grabbing the bit field.
- *
- * Examples
- *
- *  uint64_t value = getBitField(data, 2, 4);
- *
- * Returns the value of the requested bit field.
- */
-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.
- *
- * data - a byte array with size at least startPos + numBits.
- * value - the value to set in the bit field.
- * startPos - the starting index of the bit field (beginning from 0).
- */
-void setBitField(uint64_t* data, uint64_t value, const uint16_t startPos,
-        const uint16_t numBits);
-
-/* Public: Retreive the nth byte out of 8 bytes in a uint64_t.
- *
- * source - the source data to retreive the byte from.
- * byteNum - the index of the byte, starting at 0 and assuming big-endian order.
- *
- * Returns the requested byte from the source bytes.
- */
-uint8_t nthByte(const uint64_t source, const uint16_t byteNum);
-
 #ifdef __cplusplus
 }
 #endif