descriptor: Minor improvements to the parse_descriptor() function

Change the type of the source pointer to 'void' so that callers need not
cast to 'unsigned char'. Also change working types to 'uint8_t' to make
it explicit that we are dealing with 8-bit types.

Refactor the parsing loop to avoid unnecessary stack variables. The
generated assembly with this change is more efficient.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>

diff --git a/libusb/descriptor.c b/libusb/descriptor.c
index e4f376f..b65557f 100644 (file)
--- a/libusb/descriptor.c
+++ b/libusb/descriptor.c
@@ -30,41 +30,47 @@
  * for detected devices
  */
 
-static void parse_descriptor(const unsigned char *source, const char *descriptor, void *dest)
+#define READ_LE16(p) ((uint16_t)       \
+       (((uint16_t)((p)[1]) << 8) |    \
+        ((uint16_t)((p)[0]))))
+
+#define READ_LE32(p) ((uint32_t)       \
+       (((uint32_t)((p)[3]) << 24) |   \
+        ((uint32_t)((p)[2]) << 16) |   \
+        ((uint32_t)((p)[1]) <<  8) |   \
+        ((uint32_t)((p)[0]))))
+
+static void parse_descriptor(const void *source, const char *descriptor, void *dest)
 {
-       const unsigned char *sp = source;
-       unsigned char *dp = dest;
-       uint16_t w;
-       const char *cp;
-       uint32_t d;
-
-       for (cp = descriptor; *cp; cp++) {
-               switch (*cp) {
-                       case 'b':       /* 8-bit byte */
-                               *dp++ = *sp++;
-                               break;
-                       case 'w':       /* 16-bit word, convert from little endian to CPU */
-                               dp += ((uintptr_t)dp & 1);      /* Align to word boundary */
+       const uint8_t *sp = source;
+       uint8_t *dp = dest;
+       char field_type;
+
+       while (*descriptor) {
+               field_type = *descriptor++;
+               switch (field_type) {
+               case 'b':       /* 8-bit byte */
+                       *dp++ = *sp++;
+                       break;
+               case 'w':       /* 16-bit word, convert from little endian to CPU */
+                       dp += ((uintptr_t)dp & 1);      /* Align to word boundary */
 
-                               w = (uint16_t)((sp[1] << 8) | sp[0]);
-                               *((uint16_t *)dp) = w;
-                               sp += 2;
-                               dp += 2;
-                               break;
-                       case 'd':       /* 32-bit word, convert from little endian to CPU */
-                               dp += ((uintptr_t)dp & 1);      /* Align to word boundary */
-
-                               d = (uint32_t)((sp[3] << 24) | (sp[2] << 16) |
-                                                          (sp[1] << 8) | sp[0]);
-                               *((uint32_t *)dp) = d;
-                               sp += 4;
-                               dp += 4;
-                               break;
-                       case 'u':       /* 16 byte UUID */
-                               memcpy(dp, sp, 16);
-                               sp += 16;
-                               dp += 16;
-                               break;
+                       *((uint16_t *)dp) = READ_LE16(sp);
+                       sp += 2;
+                       dp += 2;
+                       break;
+               case 'd':       /* 32-bit word, convert from little endian to CPU */
+                       dp += ((uintptr_t)dp & 1);      /* Align to word boundary */
+
+                       *((uint32_t *)dp) = READ_LE32(sp);
+                       sp += 4;
+                       dp += 4;
+                       break;
+               case 'u':       /* 16 byte UUID */
+                       memcpy(dp, sp, 16);
+                       sp += 16;
+                       dp += 16;
+                       break;
                }
        }
 }
@@ -950,7 +956,7 @@ int API_EXPORTED libusb_get_usb_2_0_extension_descriptor(
        if (!_usb_2_0_extension)
                return LIBUSB_ERROR_NO_MEM;
 
-       parse_descriptor((unsigned char *)dev_cap, "bbbd", _usb_2_0_extension);
+       parse_descriptor(dev_cap, "bbbd", _usb_2_0_extension);
 
        *usb_2_0_extension = _usb_2_0_extension;
        return LIBUSB_SUCCESS;
@@ -1006,7 +1012,7 @@ int API_EXPORTED libusb_get_ss_usb_device_capability_descriptor(
        if (!_ss_usb_device_cap)
                return LIBUSB_ERROR_NO_MEM;
 
-       parse_descriptor((unsigned char *)dev_cap, "bbbbwbbw", _ss_usb_device_cap);
+       parse_descriptor(dev_cap, "bbbbwbbw", _ss_usb_device_cap);
 
        *ss_usb_device_cap = _ss_usb_device_cap;
        return LIBUSB_SUCCESS;
@@ -1062,7 +1068,7 @@ int API_EXPORTED libusb_get_container_id_descriptor(struct libusb_context *ctx,
        if (!_container_id)
                return LIBUSB_ERROR_NO_MEM;
 
-       parse_descriptor((unsigned char *)dev_cap, "bbbbu", _container_id);
+       parse_descriptor(dev_cap, "bbbbu", _container_id);
 
        *container_id = _container_id;
        return LIBUSB_SUCCESS;

diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index f2e5eaa..49b7a05 100644 (file)
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 11506
+#define LIBUSB_NANO 11507