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Port knuth_hash to odd platforms

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* src/lisp.h (hash_hash_t, knuth_hash): Use unsigned int and
unsigned long long int rather than uint32_t and uint64_t, as POSIX
does not guarantee the presence of uint64_t, and uint32_t and
uint64_t both in theory have problems with undefined behavior on
integer overflow.  This doesn’t affect behavior (or even machine
code) on typical platforms.
This commit is contained in:
Paul Eggert 2024-05-19 08:42:57 -07:00
parent c07160b8df
commit 9bcd644408
1 changed files with 9 additions and 5 deletions
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14
src/lisp.h
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@ -2534,7 +2534,7 @@ struct Lisp_Hash_Table;
/* The type of a hash value stored in the table.
It's unsigned and a subtype of EMACS_UINT. */
typedef uint32_t hash_hash_t;
typedef unsigned int hash_hash_t;
typedef enum {
Test_eql,
@ -2818,10 +2818,14 @@ INLINE ptrdiff_t
knuth_hash (hash_hash_t hash, unsigned bits)
{
/* Knuth multiplicative hashing, tailored for 32-bit indices
(avoiding a 64-bit multiply). */
uint32_t alpha = 2654435769; /* 2**32/phi */
/* Note the cast to uint64_t, to make it work for bits=0. */
return (uint64_t)((uint32_t)hash * alpha) >> (32 - bits);
(avoiding a 64-bit multiply on typical platforms). */
unsigned int h = hash;
unsigned int alpha = 2654435769; /* 2**32/phi */
/* Multiply with unsigned int, ANDing in case UINT_WIDTH exceeds 32. */
unsigned int product = (h * alpha) & 0xffffffffu;
/* Convert to a wider type, so that the shift works when BITS == 0. */
unsigned long long int wide_product = product;
return wide_product >> (32 - bits);
}