Standardize argument ordering for bitfield functions.

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

diff --git a/src/bitfield/bitfield.c b/src/bitfield/bitfield.c
index d383db0..934d5a6 100644 (file)
--- a/src/bitfield/bitfield.c
+++ b/src/bitfield/bitfield.c
@@ -1,60 +1,75 @@
 #include <bitfield/bitfield.h>
+#include <limits.h>
+#include <string.h>
+#include <stddef.h>
 
-/**
- * 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;
-}
+#define NIBBLE_SIZE (CHAR_BIT / 2)
 
-uint64_t bitmask(int numBits) {
+uint64_t bitmask(const uint8_t numBits) {
     return (((uint64_t)0x1) << numBits) - 1;
 }
 
-int startingByte(int startBit) {
-    return startBit / 8;
-}
-
-int endingByte(int startBit, int numBits) {
-    return (startBit + numBits - 1) / 8;
+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, int startBit, int numBits, bool bigEndian) {
-    int startByte = startingByte(startBit);
-    int endByte = endingByte(startBit, numBits);
-
+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);
     }
-    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];
+    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;
     }
-
-    ret >>= 8 - findEndBit(startBit, numBits);
-    return ret & bitmask(numBits);
+    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, int startBit, int numBits) {
-    int shiftDistance = 64 - startBit - numBits;
+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(uint64_t source, int byteNum) {
-    return (source >> (64 - ((byteNum + 1) * 8))) & 0xFF;
+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;
+    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 source[], const uint8_t source_length,
+        const uint8_t byte_index) {
+    if(byte_index < source_length) {
+        return source[byte_index];
+    }
+    return 0;
 }