egismoc: Use FpiByteReader to compute the check bytes

We can read the values in the proper format without having to
deal with endianness ourself, so let's do this instead of manual
labor.

1 files changed, 9 insertions, 23 deletions

diff --git a/libfprint/drivers/egismoc/egismoc.c b/libfprint/drivers/egismoc/egismoc.c
index 98bca26..336ea53 100644
--- a/libfprint/drivers/egismoc/egismoc.c
+++ b/libfprint/drivers/egismoc/egismoc.c
@@ -277,28 +277,18 @@ egismoc_cmd_ssm_done (FpiSsm   *ssm,
  * should be 0, otherwise the device will reject the payload
  */
 static guint16
-egismoc_get_check_bytes (const guchar *value,
-                         const gsize   value_length)
+egismoc_get_check_bytes (FpiByteReader *reader)
 {
   fp_dbg ("Get check bytes");
-  const size_t steps = (value_length + 1) / 2;
-  guint16 values[steps];
   size_t sum_values = 0;
+  guint16 val;
 
-  g_assert (value);
+  fpi_byte_reader_set_pos (reader, 0);
 
-  for (int i = 0, j = 0; i < value_length; i += 2, j++)
-    {
-      values[j] = (value[i] << 8 & 0xff00);
-
-      if (i < value_length - 1)
-        values[j] |= value[i + 1] & 0x00ff;
-    }
+  while (fpi_byte_reader_get_uint16_be (reader, &val))
+    sum_values += val;
 
-  for (int i = 0; i < steps; i++)
-    sum_values += values[i];
-
-  return 0xffff - (sum_values % 0xffff);
+  return G_MAXUINT16 - (sum_values % G_MAXUINT16);
 }
 
 static void
@@ -311,7 +301,6 @@ egismoc_exec_cmd (FpDevice         *device,
   g_auto(FpiByteWriter) writer = {0};
   g_autoptr(FpiUsbTransfer) transfer = NULL;
   FpiDeviceEgisMoc *self = FPI_DEVICE_EGISMOC (device);
-  const guint8 *buffer_out = NULL;
   g_autofree CommandData *data = NULL;
   gsize buffer_out_length = 0;
   gboolean written = TRUE;
@@ -331,7 +320,8 @@ egismoc_exec_cmd (FpDevice         *device,
                       + EGISMOC_CHECK_BYTES_LENGTH
                       + cmd_length;
 
-  fpi_byte_writer_init_with_size (&writer, buffer_out_length, TRUE);
+  fpi_byte_writer_init_with_size (&writer, buffer_out_length +
+                                  (buffer_out_length % 2 ? 1 : 0), TRUE);
 
   /* Prefix */
   written &= fpi_byte_writer_put_data (&writer, egismoc_write_prefix,
@@ -346,11 +336,7 @@ egismoc_exec_cmd (FpDevice         *device,
 
   /* Now fetch and set the "real" check bytes based on the currently
    * assembled payload */
-  fpi_byte_reader_set_pos (FPI_BYTE_READER (&writer), 0);
-  written &= fpi_byte_reader_peek_data (FPI_BYTE_READER (&writer),
-                                        buffer_out_length, &buffer_out);
-  check_value = egismoc_get_check_bytes (buffer_out, buffer_out_length);
-
+  check_value = egismoc_get_check_bytes (FPI_BYTE_READER (&writer));
   fpi_byte_writer_set_pos (&writer, egismoc_write_prefix_len);
   written &= fpi_byte_writer_put_uint16_be (&writer, check_value);