unaligned.h: slightly simplify get/put unaligned functions

[wimlib] / include / wimlib / unaligned.h

diff --git a/include/wimlib/unaligned.h b/include/wimlib/unaligned.h
index 5f920e75d30c5a53b39a5bdf099a176bc204b945..d25e76f6d909fb1e61ccd507956d12e56896daff 100644 (file)
--- a/include/wimlib/unaligned.h
+++ b/include/wimlib/unaligned.h
@@ -3,6 +3,9 @@
  *
  * Inline functions for unaligned memory accesses.
  *
+ * Author:     Eric Biggers
+ * Year:       2014, 2015
+ *
  * The author dedicates this file to the public domain.
  * You can do whatever you want with this file.
  */
@@ -47,63 +50,84 @@ DEFINE_UNALIGNED_TYPE(machine_word_t);
 #define store_word_unaligned   store_machine_word_t_unaligned
 
 static inline u16
-get_unaligned_u16_le(const void *p)
+get_unaligned_le16(const u8 *p)
 {
-       u16 v;
-
-       if (UNALIGNED_ACCESS_IS_FAST) {
-               v = le16_to_cpu(load_le16_unaligned(p));
-       } else {
-               const u8 *p8 = p;
-               v = 0;
-               v |= (u16)p8[0] << 0;
-               v |= (u16)p8[1] << 8;
-       }
-       return v;
+       if (UNALIGNED_ACCESS_IS_FAST)
+               return le16_to_cpu(load_le16_unaligned(p));
+       else
+               return ((u16)p[1] << 8) | p[0];
 }
 
 static inline u32
-get_unaligned_u32_le(const void *p)
+get_unaligned_le32(const u8 *p)
 {
-       u32 v;
-
-       if (UNALIGNED_ACCESS_IS_FAST) {
-               v = le32_to_cpu(load_le32_unaligned(p));
-       } else {
-               const u8 *p8 = p;
-               v = 0;
-               v |= (u32)p8[0] << 0;
-               v |= (u32)p8[1] << 8;
-               v |= (u32)p8[2] << 16;
-               v |= (u32)p8[3] << 24;
-       }
-       return v;
+       if (UNALIGNED_ACCESS_IS_FAST)
+               return le32_to_cpu(load_le32_unaligned(p));
+       else
+               return ((u32)p[3] << 24) | ((u32)p[2] << 16) |
+                       ((u32)p[1] << 8) | p[0];
 }
 
 static inline void
-put_unaligned_u16_le(u16 v, void *p)
+put_unaligned_le16(u16 v, u8 *p)
 {
        if (UNALIGNED_ACCESS_IS_FAST) {
                store_le16_unaligned(cpu_to_le16(v), p);
        } else {
-               u8 *p8 = p;
-               p8[0] = (v >> 0) & 0xFF;
-               p8[1] = (v >> 8) & 0xFF;
+               p[0] = (u8)(v >> 0);
+               p[1] = (u8)(v >> 8);
        }
 }
 
 static inline void
-put_unaligned_u32_le(u32 v, void *p)
+put_unaligned_le32(u32 v, u8 *p)
 {
        if (UNALIGNED_ACCESS_IS_FAST) {
                store_le32_unaligned(cpu_to_le32(v), p);
        } else {
-               u8 *p8 = p;
-               p8[0] = (v >> 0) & 0xFF;
-               p8[1] = (v >> 8) & 0xFF;
-               p8[2] = (v >> 16) & 0xFF;
-               p8[3] = (v >> 24) & 0xFF;
+               p[0] = (u8)(v >> 0);
+               p[1] = (u8)(v >> 8);
+               p[2] = (u8)(v >> 16);
+               p[3] = (u8)(v >> 24);
        }
 }
 
+/*
+ * Given a 32-bit value that was loaded with the platform's native endianness,
+ * return a 32-bit value whose high-order 8 bits are 0 and whose low-order 24
+ * bits contain the first 3 bytes, arranged in octets in a platform-dependent
+ * order, at the memory location from which the input 32-bit value was loaded.
+ */
+static inline u32
+loaded_u32_to_u24(u32 v)
+{
+       if (CPU_IS_LITTLE_ENDIAN)
+               return v & 0xFFFFFF;
+       else
+               return v >> 8;
+}
+
+/*
+ * Load the next 3 bytes from the memory location @p into the 24 low-order bits
+ * of a 32-bit value.  The order in which the 3 bytes will be arranged as octets
+ * in the 24 bits is platform-dependent.  At least LOAD_U24_REQUIRED_NBYTES
+ * bytes must be available at @p; note that this may be more than 3.
+ */
+static inline u32
+load_u24_unaligned(const u8 *p)
+{
+#if UNALIGNED_ACCESS_IS_FAST
+#  define LOAD_U24_REQUIRED_NBYTES 4
+       return loaded_u32_to_u24(load_u32_unaligned(p));
+#else
+#  define LOAD_U24_REQUIRED_NBYTES 3
+#  if CPU_IS_BIG_ENDIAN
+       return ((u32)p[2] << 0) | ((u32)p[1] << 8) | ((u32)p[0] << 16);
+#  else
+       return ((u32)p[0] << 0) | ((u32)p[1] << 8) | ((u32)p[2] << 16);
+#  endif
+#endif
+}
+
+
 #endif /* _WIMLIB_UNALIGNED_H */