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HashFunctions: constexpr capability

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Problem:
- Hash functions can be `constexpr`, but are not.

Solution:
- Change `inline` keyword to `constexpr`.
- Add `static_assert` tests to ensure the hash functions work in a
  `constexpr` context.
This commit is contained in:
Lenny Maiorani 2020-10-21 09:39:54 -04:00 committed by Andreas Kling
parent 070fc69562
commit 18a40587ea
Notes: sideshowbarker 2024-07-19 01:49:31 +09:00 
Author: https://github.com/ldm5180
Commit: https://github.com/SerenityOS/serenity/commit/18a40587eae
Pull-request: https://github.com/SerenityOS/serenity/pull/3813
2 changed files with 26 additions and 16 deletions
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16
AK/HashFunctions.h
View file

@ -28,7 +28,7 @@
#include "Types.h" #include "Types.h"
inline unsigned int_hash(u32 key) constexpr unsigned int_hash(u32 key)
{ {
key += ~(key << 15); key += ~(key << 15);
key ^= (key >> 10); key ^= (key >> 10);
@ -39,7 +39,7 @@ inline unsigned int_hash(u32 key)
return key; return key;
} }
inline unsigned double_hash(u32 key) constexpr unsigned double_hash(u32 key)
{ {
key = ~key + (key >> 23); key = ~key + (key >> 23);
key ^= (key << 12); key ^= (key << 12);
@ -49,27 +49,27 @@ inline unsigned double_hash(u32 key)
return key; return key;
} }
inline unsigned pair_int_hash(u32 key1, u32 key2) constexpr unsigned pair_int_hash(u32 key1, u32 key2)
{ {
return int_hash((int_hash(key1) * 209) ^ (int_hash(key2 * 413))); return int_hash((int_hash(key1) * 209) ^ (int_hash(key2 * 413)));
} }
inline unsigned u64_hash(u64 key) constexpr unsigned u64_hash(u64 key)
{ {
u32 first = key & 0xFFFFFFFF; u32 first = key & 0xFFFFFFFF;
u32 last = key >> 32; u32 last = key >> 32;
return pair_int_hash(first, last); return pair_int_hash(first, last);
} }
inline unsigned ptr_hash(FlatPtr ptr) constexpr unsigned ptr_hash(FlatPtr ptr)
{ {
if constexpr (sizeof(ptr) == 8) if constexpr (sizeof(ptr) == 8)
return u64_hash((u64)ptr); return u64_hash(ptr);
else else
return int_hash((u32)ptr); return int_hash(ptr);
} }
inline unsigned ptr_hash(const void* ptr) inline unsigned ptr_hash(const void* ptr)
{ {
return ptr_hash((FlatPtr)(ptr)); return ptr_hash(FlatPtr(ptr));
} }

26
AK/Tests/TestHashFunctions.cpp
View file

@ -31,30 +31,32 @@
TEST_CASE(int_hash) TEST_CASE(int_hash)
{ {
EXPECT_EQ(int_hash(42), 3564735745u); static_assert(int_hash(42) == 3564735745u);
EXPECT_EQ(int_hash(0), 1177991625u); static_assert(int_hash(0) == 1177991625u);
} }
TEST_CASE(double_hash) TEST_CASE(double_hash)
{ {
EXPECT_EQ(double_hash(42), 524450u); static_assert(double_hash(42) == 524450u);
EXPECT_EQ(double_hash(0), 12384u); static_assert(double_hash(0) == 12384u);
} }
TEST_CASE(pair_int_hash) TEST_CASE(pair_int_hash)
{ {
EXPECT_EQ(pair_int_hash(42, 17), 339337046u); static_assert(pair_int_hash(42, 17) == 339337046u);
EXPECT_EQ(pair_int_hash(0, 0), 954888656u); static_assert(pair_int_hash(0, 0) == 954888656u);
} }
TEST_CASE(u64_hash) TEST_CASE(u64_hash)
{ {
EXPECT_EQ(u64_hash(42), 2824066580u); static_assert(u64_hash(42) == 2824066580u);
EXPECT_EQ(u64_hash(0), 954888656u); static_assert(u64_hash(0) == 954888656u);
} }
TEST_CASE(ptr_hash) TEST_CASE(ptr_hash)
{ {
// These tests are not static_asserts because the values are
// different and the goal is to bind the behavior.
if constexpr (sizeof(FlatPtr) == 8) { if constexpr (sizeof(FlatPtr) == 8) {
EXPECT_EQ(ptr_hash(FlatPtr(42)), 2824066580u); EXPECT_EQ(ptr_hash(FlatPtr(42)), 2824066580u);
EXPECT_EQ(ptr_hash(FlatPtr(0)), 954888656u); EXPECT_EQ(ptr_hash(FlatPtr(0)), 954888656u);
@ -70,4 +72,12 @@ TEST_CASE(ptr_hash)
} }
} }
TEST_CASE(constexpr_ptr_hash)
{
// This test does not check the result because the goal is just to
// ensure the function can be executed in a constexpr context. The
// "ptr_hash" test binds the result.
static_assert(ptr_hash(FlatPtr(42)));
}
TEST_MAIN(HashFunctions) TEST_MAIN(HashFunctions)