104 lines
2.5 KiB
C
104 lines
2.5 KiB
C
/* The generic hashing primitive */
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#include "mlvalues.h"
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#include "memory.h"
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#include "str.h"
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static unsigned long hash_accu;
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static long hash_univ_limit, hash_univ_count;
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static void hash_aux();
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value hash_univ_param(count, limit, obj) /* ML */
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value obj, count, limit;
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{
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hash_univ_limit = Long_val(limit);
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hash_univ_count = Long_val(count);
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hash_accu = 0;
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hash_aux(obj);
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return Val_long(hash_accu & 0x3FFFFFFF);
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/* The & has two purposes: ensure that the return value is positive
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and give the same result on 32 bit and 64 bit architectures. */
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}
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#define Alpha 65599
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#define Beta 19
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#define Combine(new) (hash_accu = hash_accu * Alpha + (new))
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#define Combine_small(new) (hash_accu = hash_accu * Beta + (new))
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static void hash_aux(obj)
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value obj;
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{
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unsigned char * p;
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mlsize_t i;
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tag_t tag;
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hash_univ_limit--;
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if (hash_univ_count < 0 || hash_univ_limit < 0) return;
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if (Is_long(obj)) {
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hash_univ_count--;
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Combine(Long_val(obj));
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return;
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}
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/* Atoms are not in the heap, but it's better to hash their tag
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than to do nothing. */
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if (Is_atom(obj)) {
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tag = Tag_val(obj);
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hash_univ_count--;
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Combine_small(tag);
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return;
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}
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/* Pointers into the heap are well-structured blocks.
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We can inspect the block contents. */
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if (Is_in_heap(obj) || Is_young(obj)) {
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tag = Tag_val(obj);
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switch (tag) {
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case String_tag:
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hash_univ_count--;
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i = string_length(obj);
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for (p = &Byte_u(obj, 0); i > 0; i--, p++)
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Combine_small(*p);
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break;
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case Double_tag:
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/* For doubles, we inspect their binary representation, LSB first.
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The results are consistent among all platforms with IEEE floats. */
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hash_univ_count--;
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#ifdef BIG_ENDIAN
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for (p = &Byte_u(obj, sizeof(double) - 1), i = sizeof(double);
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i > 0;
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p--, i--)
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#else
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for (p = &Byte_u(obj, 0), i = sizeof(double);
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i > 0;
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p++, i--)
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#endif
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Combine_small(*p);
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break;
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case Abstract_tag:
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case Final_tag:
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/* We don't know anything about the contents of the block.
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Better do nothing. */
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break;
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default:
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hash_univ_count--;
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Combine_small(tag);
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i = Wosize_val(obj);
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while (i != 0) {
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i--;
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hash_aux(Field(obj, i));
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}
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break;
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}
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return;
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}
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/* Otherwise, obj is a pointer outside the heap, to an object with
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a priori unknown structure. Use its physical address as hash key. */
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Combine((long) obj);
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}
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