--- a/mfbt/HashFunctions.h
+++ b/mfbt/HashFunctions.h
@@ -2,16 +2,51 @@
* vim: set ts=8 sw=4 et tw=99 ft=cpp:
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at http://mozilla.org/MPL/2.0/. */
/* Utilities for hashing */
+/*
+ * This file exports functions for hashing data down to a 32-bit value,
+ * including:
+ *
+ * - HashString Hash a char* or uint16_t/wchar_t* of known or unknown
+ * length.
+ *
+ * - HashBytes Hash a byte array of known length.
+ *
+ * - HashGeneric Hash one or more values. Currently, we support uint32_t,
+ * types which can be implicitly cast to uint32_t, data
+ * pointers, and function pointers.
+ *
+ * - AddToHash Add one or more values to the given hash. This supports the
+ * same list of types as HashGeneric.
+ *
+ *
+ * You can chain these functions together to hash complex objects. For example:
+ *
+ * class ComplexObject {
+ * char* str;
+ * uint32_t uint1, uint2;
+ * void (*callbackFn)();
+ *
+ * uint32_t Hash() {
+ * uint32_t hash = HashString(str);
+ * hash = AddToHash(hash, uint1, uint2);
+ * return AddToHash(hash, callbackFn);
+ * }
+ * };
+ *
+ * If you want to hash an nsAString or nsACString, use the HashString functions
+ * in nsHashKey.h.
+ */
+
#ifndef mozilla_HashFunctions_h_
#define mozilla_HashFunctions_h_
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/StandardInteger.h"
#ifdef __cplusplus
@@ -24,28 +59,25 @@ static const uint32_t GoldenRatioU32 = 0
inline uint32_t
RotateLeft32(uint32_t value, uint8_t bits)
{
MOZ_ASSERT(bits < 32);
return (value << bits) | (value >> (32 - bits));
}
-/**
- * Add the given value(s) to the given hashcode and return the new hashcode.
- *
- * AddToHash(h, x, y) is equivalent to AddToHash(AddToHash(h, x), y).
- */
-MOZ_WARN_UNUSED_RESULT
+namespace detail {
+
inline uint32_t
-AddToHash(uint32_t hash, uint32_t value)
+AddU32ToHash(uint32_t hash, uint32_t value)
{
/*
- * This is not a sophisticated hash routine, but it seems to work well for our
- * mostly plain-text inputs. Implementation notes follow.
+ * This is the meat of all our hash routines. This hash function is not
+ * particularly sophisticated, but it seems to work well for our mostly
+ * plain-text inputs. Implementation notes follow.
*
* Our use of the golden ratio here is arbitrary; we could pick almost any
* number which:
*
* * is odd (because otherwise, all our hash values will be even)
*
* * has a reasonably-even mix of 1's and 0's (consider the extreme case
* where we multiply by 0x3 or 0xeffffff -- this will not produce good
@@ -53,60 +85,266 @@ AddToHash(uint32_t hash, uint32_t value)
*
* The rotation length of 5 is also arbitrary, although an odd number is again
* preferable so our hash explores the whole universe of possible rotations.
*
* Finally, we multiply by the golden ratio *after* xor'ing, not before.
* Otherwise, if |hash| is 0 (as it often is for the beginning of a message),
* the expression
*
- * (GoldenRatioU32 * RotateLeft(hash, 5)) ^ value
+ * (GoldenRatioU32 * RotateLeft(hash, 5)) |xor| value
*
* evaluates to |value|.
*
* (Number-theoretic aside: Because any odd number |m| is relatively prime to
* our modulus (2^32), the list
*
* [x * m (mod 2^32) for 0 <= x < 2^32]
*
* has no duplicate elements. This means that multiplying by |m| does not
* cause us to skip any possible hash values.
*
- * It's also nice if |m| has larger order mod 2^32 -- that is, if the smallest
- * k such that m^k == 1 (mod 2^32) is large -- so we can safely multiply our
- * hash value by |m| a few times without negating the multiplicative effect.
- * Our golden ratio constant has order 2^29, which is more than enough for our
- * purposes.)
+ * It's also nice if |m| has large-ish order mod 2^32 -- that is, if the
+ * smallest k such that m^k == 1 (mod 2^32) is large -- so we can safely
+ * multiply our hash value by |m| a few times without negating the
+ * multiplicative effect. Our golden ratio constant has order 2^29, which is
+ * more than enough for our purposes.)
*/
return GoldenRatioU32 * (RotateLeft32(hash, 5) ^ value);
}
+/**
+ * AddUintptrToHash takes sizeof(uintptr_t) as a template parameter.
+ */
+template<size_t PtrSize>
+inline uint32_t
+AddUintptrToHash(uint32_t hash, uintptr_t value);
+
+template<>
+inline uint32_t
+AddUintptrToHash<4>(uint32_t hash, uintptr_t value)
+{
+ return AddU32ToHash(hash, static_cast<uint32_t>(value));
+}
+
+template<>
+inline uint32_t
+AddUintptrToHash<8>(uint32_t hash, uintptr_t value)
+{
+ /*
+ * The static cast to uint64_t below is necessary because this function
+ * sometimes gets compiled on 32-bit platforms (yes, even though it's a
+ * template and we never call this particular override in a 32-bit build). If
+ * we do value >> 32 on a 32-bit machine, we're shifting a 32-bit uintptr_t
+ * right 32 bits, and the compiler throws an error.
+ */
+ uint32_t v1 = static_cast<uint32_t>(value);
+ uint32_t v2 = static_cast<uint32_t>(static_cast<uint64_t>(value) >> 32);
+ return AddU32ToHash(AddU32ToHash(hash, v1), v2);
+}
+
+} /* namespace detail */
+
+/**
+ * AddToHash takes a hash and some values and returns a new hash based on the
+ * inputs.
+ *
+ * Currently, we support hashing uint32_t's, values which we can implicitly
+ * convert to uint32_t, data pointers, and function pointers.
+ */
+template<typename A>
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+AddToHash(uint32_t hash, A a)
+{
+ /*
+ * Try to convert |A| to uint32_t implicitly. If this works, great. If not,
+ * we'll error out.
+ */
+ return detail::AddU32ToHash(hash, a);
+}
+
+template<typename A>
MOZ_WARN_UNUSED_RESULT
inline uint32_t
-AddToHash(uint32_t hash, uint32_t v1, uint32_t v2)
+AddToHash(uint32_t hash, A* a)
+{
+ /*
+ * You might think this function should just take a void*. But then we'd only
+ * catch data pointers and couldn't handle function pointers.
+ */
+
+ MOZ_STATIC_ASSERT(sizeof(a) == sizeof(uintptr_t),
+ "Strange pointer!");
+
+ return detail::AddUintptrToHash<sizeof(uintptr_t)>(hash, uintptr_t(a));
+}
+
+template<typename A, typename B>
+MOZ_WARN_UNUSED_RESULT
+uint32_t
+AddToHash(uint32_t hash, A a, B b)
+{
+ return AddToHash(AddToHash(hash, a), b);
+}
+
+template<typename A, typename B, typename C>
+MOZ_WARN_UNUSED_RESULT
+uint32_t
+AddToHash(uint32_t hash, A a, B b, C c)
+{
+ return AddToHash(AddToHash(hash, a, b), c);
+}
+
+template<typename A, typename B, typename C, typename D>
+MOZ_WARN_UNUSED_RESULT
+uint32_t
+AddToHash(uint32_t hash, A a, B b, C c, D d)
+{
+ return AddToHash(AddToHash(hash, a, b, c), d);
+}
+
+template<typename A, typename B, typename C, typename D, typename E>
+MOZ_WARN_UNUSED_RESULT
+uint32_t
+AddToHash(uint32_t hash, A a, B b, C c, D d, E e)
+{
+ return AddToHash(AddToHash(hash, a, b, c, d), e);
+}
+
+/**
+ * The HashGeneric class of functions let you hash one or more values.
+ *
+ * If you want to hash together two values x and y, calling HashGeneric(x, y) is
+ * much better than calling AddToHash(x, y), because AddToHash(x, y) assumes
+ * that x has already been hashed.
+ */
+template<typename A>
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashGeneric(A a)
{
- return AddToHash(AddToHash(hash, v1), v2);
+ return AddToHash(0, a);
+}
+
+template<typename A, typename B>
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashGeneric(A a, B b)
+{
+ return AddToHash(0, a, b);
+}
+
+template<typename A, typename B, typename C>
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashGeneric(A a, B b, C c)
+{
+ return AddToHash(0, a, b, c);
+}
+
+template<typename A, typename B, typename C, typename D>
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashGeneric(A a, B b, C c, D d)
+{
+ return AddToHash(0, a, b, c, d);
+}
+
+template<typename A, typename B, typename C, typename D, typename E>
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashGeneric(A a, B b, C c, D d, E e)
+{
+ return AddToHash(0, a, b, c, d, e);
+}
+
+namespace detail {
+
+template<typename T>
+uint32_t
+HashUntilZero(const T* str)
+{
+ uint32_t hash = 0;
+ for (T c; (c = *str); str++)
+ hash = AddToHash(hash, c);
+ return hash;
+}
+
+template<typename T>
+uint32_t
+HashKnownLength(const T* str, size_t length)
+{
+ uint32_t hash = 0;
+ for (size_t i = 0; i < length; i++)
+ hash = AddToHash(hash, str[i]);
+ return hash;
+}
+
+} /* namespace detail */
+
+/**
+ * The HashString overloads below do just what you'd expect.
+ *
+ * If you have the string's length, you might as well call the overload which
+ * includes the length. It may be marginally faster.
+ */
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashString(const char* str)
+{
+ return detail::HashUntilZero(str);
}
MOZ_WARN_UNUSED_RESULT
inline uint32_t
-AddToHash(uint32_t hash, uint32_t v1, uint32_t v2, uint32_t v3)
+HashString(const char* str, size_t length)
{
- return AddToHash(AddToHash(hash, v1, v2), v3);
+ return detail::HashKnownLength(str, length);
+}
+
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashString(const uint16_t* str)
+{
+ return detail::HashUntilZero(str);
}
MOZ_WARN_UNUSED_RESULT
inline uint32_t
-AddToHash(uint32_t hash, uint32_t v1, uint32_t v2, uint32_t v3, uint32_t v4)
+HashString(const uint16_t* str, size_t length)
{
- return AddToHash(AddToHash(hash, v1, v2, v3), v4);
+ return detail::HashKnownLength(str, length);
+}
+
+/*
+ * On Windows, wchar_t (PRUnichar) is not the same as uint16_t, even though it's
+ * the same width!
+ */
+#ifdef WIN32
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashString(const wchar_t* str)
+{
+ return detail::HashUntilZero(str);
}
MOZ_WARN_UNUSED_RESULT
inline uint32_t
-AddToHash(uint32_t hash, uint32_t v1, uint32_t v2, uint32_t v3, uint32_t v4, uint32_t v5)
+HashString(const wchar_t* str, size_t length)
{
- return AddToHash(AddToHash(hash, v1, v2, v3, v4), v5);
+ return detail::HashKnownLength(str, length);
}
+#endif
+
+/**
+ * Hash some number of bytes.
+ *
+ * This hash walks word-by-word, rather than byte-by-byte, so you won't get the
+ * same result out of HashBytes as you would out of HashString.
+ */
+MOZ_WARN_UNUSED_RESULT
+extern MFBT_API(uint32_t)
+HashBytes(const void* bytes, size_t length);
} /* namespace mozilla */
#endif /* __cplusplus */
#endif /* mozilla_HashFunctions_h_ */