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Remove the misguided extension here that reserved two special values in

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the hash_code. I'm not sure what I was thinking here, the use cases for
special values are in the *keys*, not in the hashes of those keys.

We can always resurrect this if needed, or clients can accomplish the
same goal themselves. This makes the general case somewhat faster (~5
cycles faster on my machine) and smaller with less branching.

llvm-svn: 151865
This commit is contained in:
Chandler Carruth 2012-03-02 00:48:38 +00:00
parent 39493f0f97
commit e07f473768
2 changed files with 17 additions and 61 deletions
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66
include/llvm/ADT/Hashing.h
View File

@ -82,35 +82,16 @@ class hash_code {
size_t value;
public:
/// \brief Default construct a hash_code. Constructs a null code.
hash_code() : value() {}
/// \brief Default construct a hash_code.
/// Note that this leaves the value uninitialized.
hash_code() {}
/// \brief Form a hash code directly from a numerical value.
hash_code(size_t value) : value(value) {
// Ensure we don't form a hash_code with one of the prohibited values.
assert(value != get_null_code().value);
assert(value != get_invalid_code().value);
}
hash_code(size_t value) : value(value) {}
/// \brief Convert the hash code to its numerical value for use.
/*explicit*/ operator size_t() const { return value; }
/// \brief Get a hash_code object which corresponds to a null code.
///
/// The null code must never be the result of any 'hash_value' calls and can
/// be used to detect an unset hash_code.
static hash_code get_null_code() { return hash_code(); }
/// \brief Get a hash_code object which corresponds to an invalid code.
///
/// The invalid code must never be the result of any 'hash_value' calls. This
/// can be used to flag invalid hash_codes or mark entries in a hash table.
static hash_code get_invalid_code() {
hash_code invalid_code;
invalid_code.value = static_cast<size_t>(-1);
return invalid_code;
}
friend bool operator==(const hash_code &lhs, const hash_code &rhs) {
return lhs.value == rhs.value;
}
@ -223,27 +204,18 @@ inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) {
}
inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) {
uint64_t hash;
if (length >= 4 && length <= 8)
hash = hash_4to8_bytes(s, length, seed);
else if (length > 8 && length <= 16)
hash = hash_9to16_bytes(s, length, seed);
else if (length > 16 && length <= 32)
hash = hash_17to32_bytes(s, length, seed);
else if (length > 32)
hash = hash_33to64_bytes(s, length, seed);
else if (length != 0)
hash = hash_1to3_bytes(s, length, seed);
else
return k2 ^ seed;
return hash_4to8_bytes(s, length, seed);
if (length > 8 && length <= 16)
return hash_9to16_bytes(s, length, seed);
if (length > 16 && length <= 32)
return hash_17to32_bytes(s, length, seed);
if (length > 32)
return hash_33to64_bytes(s, length, seed);
if (length != 0)
return hash_1to3_bytes(s, length, seed);
// FIXME: The invalid hash_code check is really expensive; there should be
// a better way of ensuring these invariants hold.
if (hash == static_cast<uint64_t>(hash_code::get_null_code()))
hash = k1 ^ seed;
else if (hash == static_cast<uint64_t>(hash_code::get_invalid_code()))
hash = k3 ^ seed;
return hash;
return k2 ^ seed;
}
/// \brief The intermediate state used during hashing.
@ -299,14 +271,8 @@ struct hash_state {
/// \brief Compute the final 64-bit hash code value based on the current
/// state and the length of bytes hashed.
uint64_t finalize(size_t length) {
uint64_t final_value
= hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2,
hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0);
if (final_value == static_cast<uint64_t>(hash_code::get_null_code()))
final_value = k1 ^ seed;
if (final_value == static_cast<uint64_t>(hash_code::get_invalid_code()))
final_value = k3 ^ seed;
return final_value;
return hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2,
hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0);
}
};

12
unittests/ADT/HashingTest.cpp
View File

@ -53,7 +53,6 @@ TEST(HashingTest, HashValueBasicTest) {
EXPECT_EQ(hash_value(42), hash_value(x));
EXPECT_NE(hash_value(42), hash_value(y));
EXPECT_NE(hash_value(42), hash_value(p));
EXPECT_NE(hash_code::get_null_code(), hash_value(p));
EXPECT_EQ(hash_value(71), hash_value(i));
EXPECT_EQ(hash_value(71), hash_value(ci));
EXPECT_EQ(hash_value(71), hash_value(vi));
@ -75,13 +74,10 @@ TEST(HashingTest, HashCombineRangeBasicTest) {
// Leave this uninitialized in the hope that valgrind will catch bad reads.
int dummy;
hash_code dummy_hash = hash_combine_range(&dummy, &dummy);
EXPECT_NE(hash_code::get_null_code(), dummy_hash);
EXPECT_NE(hash_code::get_invalid_code(), dummy_hash);
EXPECT_NE(hash_code(0), dummy_hash);
const int arr1[] = { 1, 2, 3 };
hash_code arr1_hash = hash_combine_range(begin(arr1), end(arr1));
EXPECT_NE(hash_code::get_null_code(), arr1_hash);
EXPECT_NE(hash_code::get_invalid_code(), arr1_hash);
EXPECT_NE(dummy_hash, arr1_hash);
EXPECT_EQ(arr1_hash, hash_combine_range(begin(arr1), end(arr1)));
@ -96,22 +92,16 @@ TEST(HashingTest, HashCombineRangeBasicTest) {
const int arr2[] = { 3, 2, 1 };
hash_code arr2_hash = hash_combine_range(begin(arr2), end(arr2));
EXPECT_NE(hash_code::get_null_code(), arr2_hash);
EXPECT_NE(hash_code::get_invalid_code(), arr2_hash);
EXPECT_NE(dummy_hash, arr2_hash);
EXPECT_NE(arr1_hash, arr2_hash);
const int arr3[] = { 1, 1, 2, 3 };
hash_code arr3_hash = hash_combine_range(begin(arr3), end(arr3));
EXPECT_NE(hash_code::get_null_code(), arr3_hash);
EXPECT_NE(hash_code::get_invalid_code(), arr3_hash);
EXPECT_NE(dummy_hash, arr3_hash);
EXPECT_NE(arr1_hash, arr3_hash);
const int arr4[] = { 1, 2, 3, 3 };
hash_code arr4_hash = hash_combine_range(begin(arr4), end(arr4));
EXPECT_NE(hash_code::get_null_code(), arr4_hash);
EXPECT_NE(hash_code::get_invalid_code(), arr4_hash);
EXPECT_NE(dummy_hash, arr4_hash);
EXPECT_NE(arr1_hash, arr4_hash);