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Merge pull request #400 from protobuf-c/ilya-zigzag

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protobuf-c.c: Make zigzag encoding more compact
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Robert Edmonds 2019-10-18 21:21:27 -04:00 committed by GitHub
commit ef868b712f
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1 changed files with 10 additions and 16 deletions
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protobuf-c/protobuf-c.c
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@ -312,10 +312,9 @@ int32_size(int32_t v)
static inline uint32_t static inline uint32_t
zigzag32(int32_t v) zigzag32(int32_t v)
{ {
if (v < 0) // Note: the right-shift must be arithmetic
return (-(uint32_t)v) * 2 - 1; // Note: left shift must be unsigned because of overflow
else return ((uint32_t)(v) << 1) ^ (uint32_t)(v >> 31);
return (uint32_t)(v) * 2;
} }
/** /**
@ -377,10 +376,9 @@ uint64_size(uint64_t v)
static inline uint64_t static inline uint64_t
zigzag64(int64_t v) zigzag64(int64_t v)
{ {
if (v < 0) // Note: the right-shift must be arithmetic
return (-(uint64_t)v) * 2 - 1; // Note: left shift must be unsigned because of overflow
else return ((uint64_t)(v) << 1) ^ (uint64_t)(v >> 63);
return (uint64_t)(v) * 2;
} }
/** /**
@ -2423,10 +2421,8 @@ parse_int32(unsigned len, const uint8_t *data)
static inline int32_t static inline int32_t
unzigzag32(uint32_t v) unzigzag32(uint32_t v)
{ {
if (v & 1) // Note: Using unsigned types prevents undefined behavior
return -(v >> 1) - 1; return (int32_t)((v >> 1) ^ (~(v & 1) + 1));
else
return v >> 1;
} }
static inline uint32_t static inline uint32_t
@ -2467,10 +2463,8 @@ parse_uint64(unsigned len, const uint8_t *data)
static inline int64_t static inline int64_t
unzigzag64(uint64_t v) unzigzag64(uint64_t v)
{ {
if (v & 1) // Note: Using unsigned types prevents undefined behavior
return -(v >> 1) - 1; return (int64_t)((v >> 1) ^ (~(v & 1) + 1));
else
return v >> 1;
} }
static inline uint64_t static inline uint64_t