From: Shawn Landden <slandden@gmail.com>
Date: Sun, 17 Dec 2017 05:44:56 +0000 (-0800)
Subject: unaligned: let gcc generate optimal code
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=commitdiff_plain;h=858cb114af3be21b7ba094efd5df65d3869a8ab1;p=elogind.git

unaligned: let gcc generate optimal code

on some architectures such as MIPS there are special unaligned load/store
sequences, instead of having to do bitwise accesses

https://www.linux-mips.org/wiki/Alignment
---

diff --git a/src/basic/unaligned.h b/src/basic/unaligned.h
index 201b3d227..73302b423 100644
--- a/src/basic/unaligned.h
+++ b/src/basic/unaligned.h
@@ -26,89 +26,77 @@
 /* BE */
 
 static inline uint16_t unaligned_read_be16(const void *_u) {
-        const uint8_t *u = _u;
+        const struct __attribute__((packed, may_alias)) { uint16_t x; } *u = _u;
 
-        return (((uint16_t) u[0]) << 8) |
-                ((uint16_t) u[1]);
+        return be16toh(u->x);
 }
 
 static inline uint32_t unaligned_read_be32(const void *_u) {
-        const uint8_t *u = _u;
+        const struct __attribute__((packed, may_alias)) { uint32_t x; } *u = _u;
 
-        return (((uint32_t) unaligned_read_be16(u)) << 16) |
-                ((uint32_t) unaligned_read_be16(u + 2));
+        return be32toh(u->x);
 }
 
 static inline uint64_t unaligned_read_be64(const void *_u) {
-        const uint8_t *u = _u;
+        const struct __attribute__((packed, may_alias)) { uint64_t x; } *u = _u;
 
-        return (((uint64_t) unaligned_read_be32(u)) << 32) |
-                ((uint64_t) unaligned_read_be32(u + 4));
+        return be64toh(u->x);
 }
 
 static inline void unaligned_write_be16(void *_u, uint16_t a) {
-        uint8_t *u = _u;
+        struct __attribute__((packed, may_alias)) { uint16_t x; } *u = _u;
 
-        u[0] = (uint8_t) (a >> 8);
-        u[1] = (uint8_t) a;
+        u->x = be16toh(a);
 }
 
 static inline void unaligned_write_be32(void *_u, uint32_t a) {
-        uint8_t *u = _u;
+        struct __attribute__((packed, may_alias)) { uint32_t x; } *u = _u;
 
-        unaligned_write_be16(u, (uint16_t) (a >> 16));
-        unaligned_write_be16(u + 2, (uint16_t) a);
+        u->x = be32toh(a);
 }
 
 static inline void unaligned_write_be64(void *_u, uint64_t a) {
-        uint8_t *u = _u;
+        struct __attribute__((packed, may_alias)) { uint64_t x; } *u = _u;
 
-        unaligned_write_be32(u, (uint32_t) (a >> 32));
-        unaligned_write_be32(u + 4, (uint32_t) a);
+        u->x = be64toh(a);
 }
 
 /* LE */
 
 static inline uint16_t unaligned_read_le16(const void *_u) {
-        const uint8_t *u = _u;
+        const struct __attribute__((packed, may_alias)) { uint16_t x; } *u = _u;
 
-        return (((uint16_t) u[1]) << 8) |
-                ((uint16_t) u[0]);
+        return le16toh(u->x);
 }
 
 static inline uint32_t unaligned_read_le32(const void *_u) {
-        const uint8_t *u = _u;
+        const struct __attribute__((packed, may_alias)) { uint32_t x; } *u = _u;
 
-        return (((uint32_t) unaligned_read_le16(u + 2)) << 16) |
-                ((uint32_t) unaligned_read_le16(u));
+        return le32toh(u->x);
 }
 
 static inline uint64_t unaligned_read_le64(const void *_u) {
-        const uint8_t *u = _u;
+        const struct __attribute__((packed, may_alias)) { uint64_t x; } *u = _u;
 
-        return (((uint64_t) unaligned_read_le32(u + 4)) << 32) |
-                ((uint64_t) unaligned_read_le32(u));
+        return le64toh(u->x);
 }
 
 static inline void unaligned_write_le16(void *_u, uint16_t a) {
-        uint8_t *u = _u;
+        struct __attribute__((packed, may_alias)) { uint16_t x; } *u = _u;
 
-        u[0] = (uint8_t) a;
-        u[1] = (uint8_t) (a >> 8);
+        u->x = le16toh(a);
 }
 
 static inline void unaligned_write_le32(void *_u, uint32_t a) {
-        uint8_t *u = _u;
+        struct __attribute__((packed, may_alias)) { uint32_t x; } *u = _u;
 
-        unaligned_write_le16(u, (uint16_t) a);
-        unaligned_write_le16(u + 2, (uint16_t) (a >> 16));
+        u->x = le32toh(a);
 }
 
 static inline void unaligned_write_le64(void *_u, uint64_t a) {
-        uint8_t *u = _u;
+        struct __attribute__((packed, may_alias)) { uint64_t x; } *u = _u;
 
-        unaligned_write_le32(u, (uint32_t) a);
-        unaligned_write_le32(u + 4, (uint32_t) (a >> 32));
+        u->x = le64toh(a);
 }
 
 #if __BYTE_ORDER == __BIG_ENDIAN