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-rw-r--r--libguile/cache-internal.h110
1 files changed, 110 insertions, 0 deletions
diff --git a/libguile/cache-internal.h b/libguile/cache-internal.h
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+++ b/libguile/cache-internal.h
@@ -0,0 +1,110 @@
+#ifndef SCM_CACHE_INTERNAL_H
+#define SCM_CACHE_INTERNAL_H
+
+/* Copyright 2016,2018
+ Free Software Foundation, Inc.
+
+ This file is part of Guile.
+
+ Guile is free software: you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published
+ by the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ Guile is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with Guile. If not, see
+ <https://www.gnu.org/licenses/>. */
+
+
+
+
+#include <string.h>
+
+#include "libguile/gc.h"
+#include "libguile/hash.h"
+
+
+/* A simple cache with 8 entries. The cache entries are stored in a
+ sorted vector. */
+struct scm_cache_entry
+{
+ scm_t_bits key;
+ scm_t_bits value;
+};
+
+#define SCM_CACHE_SIZE 16
+
+struct scm_cache
+{
+ scm_t_bits eviction_cookie;
+ struct scm_cache_entry entries[SCM_CACHE_SIZE];
+};
+
+static inline struct scm_cache*
+scm_make_cache (void)
+{
+ struct scm_cache *ret = scm_gc_typed_calloc (struct scm_cache);
+ ret->eviction_cookie = (scm_t_bits) ret;
+ return ret;
+}
+
+static inline int
+scm_cache_full_p (struct scm_cache *cache)
+{
+ return cache->entries[0].key != 0;
+}
+
+static inline void
+scm_cache_evict_1 (struct scm_cache *cache, struct scm_cache_entry *evicted)
+{
+ size_t idx;
+ cache->eviction_cookie = scm_ihashq (SCM_PACK (cache->eviction_cookie), -1);
+ idx = cache->eviction_cookie & (SCM_CACHE_SIZE - 1);
+ memcpy (evicted, cache->entries + idx, sizeof (*evicted));
+ memmove (cache->entries + 1,
+ cache->entries,
+ sizeof (cache->entries[0]) * idx);
+ cache->entries[0].key = 0;
+ cache->entries[0].value = 0;
+}
+
+static inline struct scm_cache_entry*
+scm_cache_lookup (struct scm_cache *cache, SCM k)
+{
+ scm_t_bits k_bits = SCM_UNPACK (k);
+ struct scm_cache_entry *entry = cache->entries;
+ /* Unrolled binary search, compiled to branchless cmp + cmov chain. */
+ if (entry[8].key <= k_bits) entry += 8;
+ if (entry[4].key <= k_bits) entry += 4;
+ if (entry[2].key <= k_bits) entry += 2;
+ if (entry[1].key <= k_bits) entry += 1;
+ return entry;
+}
+
+static inline void
+scm_cache_insert (struct scm_cache *cache, SCM k, SCM v,
+ struct scm_cache_entry *evicted)
+{
+ struct scm_cache_entry *entry;
+
+ if (scm_cache_full_p (cache))
+ scm_cache_evict_1 (cache, evicted);
+ entry = scm_cache_lookup (cache, k);
+ if (entry->key == SCM_UNPACK (k))
+ {
+ entry->value = SCM_UNPACK (v);
+ return;
+ }
+ memmove (cache->entries,
+ cache->entries + 1,
+ (entry - cache->entries) * sizeof (*entry));
+ entry->key = SCM_UNPACK (k);
+ entry->value = SCM_UNPACK (v);
+}
+
+#endif /* SCM_CACHE_INTERNAL_H */