Fix byte alignment for right aligned functions.

[apps/agl-service-can-low-level.git] / src / bitfield / 8byte.c

diff --git a/src/bitfield/8byte.c b/src/bitfield/8byte.c
index 0f249d9..e3eddf2 100644 (file)
--- a/src/bitfield/8byte.c
+++ b/src/bitfield/8byte.c
@@ -4,53 +4,58 @@
 #include <limits.h>
 #include <string.h>
 
-uint64_t bitmask(const uint8_t numBits) {
-    return (((uint64_t)0x1) << numBits) - 1;
+#define EIGHTBYTE_BIT (8 * sizeof(uint64_t))
+
+uint64_t bitmask(const uint8_t bit_count) {
+    return (((uint64_t)0x1) << bit_count) - 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;
+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 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);
+uint64_t get_bit_field(uint64_t source, const uint16_t offset,
+        const uint16_t bit_count, const bool big_endian) {
+    int startByte = offset / CHAR_BIT;
+    int endByte = (offset + bit_count - 1) / CHAR_BIT;
+
+    if(!big_endian) {
+        source = __builtin_bswap64(source);
     }
-    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);
+
+    uint8_t* bytes = (uint8_t*)&source;
+    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];
         }
-    } 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;
+    ret >>= 8 - find_end_bit(offset + bit_count);
+    return ret & bitmask(bit_count);
 }
 
-uint8_t nthByte(const uint64_t source, const uint16_t byteNum) {
-    return (source >> (64 - ((byteNum + 1) * CHAR_BIT))) & 0xFF;
-}
+bool set_bit_field(uint64_t* destination, uint64_t value, const uint16_t offset,
+        const uint16_t bit_count) {
+    if(value > bitmask(bit_count)) {
+        return false;
+    }
 
+    int shiftDistance = EIGHTBYTE_BIT - offset - bit_count;
+    value <<= shiftDistance;
+    *destination &= ~(bitmask(bit_count) << shiftDistance);
+    *destination |= value;
+    return true;
+}