allow buffer sizes that are not multiples of 4 in crc calculation

1 files changed, 50 insertions, 13 deletions

diff --git a/daemon/stm32crc.cpp b/daemon/stm32crc.cpp
index 2bb1def..d4e5bd9 100644
--- a/daemon/stm32crc.cpp
+++ b/daemon/stm32crc.cpp
@@ -1,5 +1,9 @@
+#include <QtEndian>
 #include "stm32crc.h"
 
+namespace
+{
+
 /** Precomputed CRC polynomial
  * Generated by pycrc v0.8.2, http://www.tty1.net/pycrc/
  * using the configuration:
@@ -12,7 +16,7 @@
  *    Algorithm    = table-driven
  * The algorithm has been modified to use 32bit word size like STM32
  *****************************************************************************/
-static const quint32 crc_table[256] = {
+const quint32 crc_table[256] = {
     0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9,
     0x130476dc, 0x17c56b6b, 0x1a864db2, 0x1e475005,
     0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
@@ -79,6 +83,20 @@ static const quint32 crc_table[256] = {
     0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4
 };
 
+const int word_len = sizeof(quint32);
+
+quint32 calc_crc(quint32 crc, quint32 word)
+{
+    crc ^= word;
+    crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
+    crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
+    crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
+    crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
+    return crc;
+}
+
+}
+
 Stm32Crc::Stm32Crc()
 {
     reset();
@@ -87,25 +105,40 @@ Stm32Crc::Stm32Crc()
 void Stm32Crc::reset()
 {
     crc = 0xFFFFFFFFU;
+    rem = 0;
+    memset(buffer, 0, word_len);
 }
 
 void Stm32Crc::addData(const char *data, int length)
 {
-    const int word_len = sizeof(quint32);
-    int i = 0;
+    int off = 0;
 
-    Q_ASSERT(length % word_len == 0);
-    Q_ASSERT(quintptr(data) % word_len == 0);
+    if (rem > 0) {
+         for (; rem < word_len && off < length; ++rem, ++off) {
+             buffer[rem] = data[off];
+         }
 
-    for (; i < (length/word_len)*word_len; i+=word_len) {
-        const quint32 *word = reinterpret_cast<const quint32*>(&data[i]);
+         Q_ASSERT(rem <= word_len);
 
-        crc ^= *word;
-        crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
-        crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
-        crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
-        crc = (crc << 8) ^ crc_table[(crc >> 24) & 0xFF];
+         if (rem == word_len) {
+             crc = calc_crc(crc, qFromLittleEndian<quint32>(buffer));
+             memset(buffer, 0, word_len);
+             rem = 0;
+         }
     }
+
+    Q_ASSERT(rem == 0 || off == length);
+
+    for (; off < (length/word_len)*word_len; off+=word_len) {
+        quint32 word = qFromLittleEndian<quint32>(reinterpret_cast<const uchar*>(&data[off]));
+        crc = calc_crc(crc, word);
+    }
+
+    for (; off < length; ++off, ++rem) {
+        buffer[rem] = data[off];
+    }
+
+    Q_ASSERT(rem <= word_len);
 }
 
 void Stm32Crc::addData(const QByteArray &data)
@@ -115,5 +148,9 @@ void Stm32Crc::addData(const QByteArray &data)
 
 quint32 Stm32Crc::result() const
 {
-    return crc;
+    if (rem > 0) {
+        return calc_crc(crc, qFromLittleEndian<quint32>(buffer));
+    } else {
+        return crc;
+    }
 }