1 files changed, 346 insertions, 0 deletions
diff --git a/prism/util/pm_constant_pool.c b/prism/util/pm_constant_pool.c
new file mode 100644
index 0000000000..2a3203f4c4
--- /dev/null
+++ b/prism/util/pm_constant_pool.c
@@ -0,0 +1,346 @@
+#include "prism/util/pm_constant_pool.h"
+
+/**
+ * Initialize a list of constant ids.
+ */
+void
+pm_constant_id_list_init(pm_constant_id_list_t *list) {
+    list->ids = NULL;
+    list->size = 0;
+    list->capacity = 0;
+}
+
+/**
+ * Initialize a list of constant ids with a given capacity.
+ */
+void
+pm_constant_id_list_init_capacity(pm_constant_id_list_t *list, size_t capacity) {
+    list->ids = xcalloc(capacity, sizeof(pm_constant_id_t));
+    if (list->ids == NULL) abort();
+
+    list->size = 0;
+    list->capacity = capacity;
+}
+
+/**
+ * Append a constant id to a list of constant ids. Returns false if any
+ * potential reallocations fail.
+ */
+bool
+pm_constant_id_list_append(pm_constant_id_list_t *list, pm_constant_id_t id) {
+    if (list->size >= list->capacity) {
+        list->capacity = list->capacity == 0 ? 8 : list->capacity * 2;
+        list->ids = (pm_constant_id_t *) xrealloc(list->ids, sizeof(pm_constant_id_t) * list->capacity);
+        if (list->ids == NULL) return false;
+    }
+
+    list->ids[list->size++] = id;
+    return true;
+}
+
+/**
+ * Insert a constant id into a list of constant ids at the specified index.
+ */
+void
+pm_constant_id_list_insert(pm_constant_id_list_t *list, size_t index, pm_constant_id_t id) {
+    assert(index < list->capacity);
+    assert(list->ids[index] == PM_CONSTANT_ID_UNSET);
+
+    list->ids[index] = id;
+    list->size++;
+}
+
+/**
+ * Checks if the current constant id list includes the given constant id.
+ */
+bool
+pm_constant_id_list_includes(pm_constant_id_list_t *list, pm_constant_id_t id) {
+    for (size_t index = 0; index < list->size; index++) {
+        if (list->ids[index] == id) return true;
+    }
+    return false;
+}
+
+/**
+ * Get the memory size of a list of constant ids.
+ */
+size_t
+pm_constant_id_list_memsize(pm_constant_id_list_t *list) {
+    return sizeof(pm_constant_id_list_t) + (list->capacity * sizeof(pm_constant_id_t));
+}
+
+/**
+ * Free the memory associated with a list of constant ids.
+ */
+void
+pm_constant_id_list_free(pm_constant_id_list_t *list) {
+    if (list->ids != NULL) {
+        xfree(list->ids);
+    }
+}
+
+/**
+ * A relatively simple hash function (djb2) that is used to hash strings. We are
+ * optimizing here for simplicity and speed.
+ */
+static inline uint32_t
+pm_constant_pool_hash(const uint8_t *start, size_t length) {
+    // This is a prime number used as the initial value for the hash function.
+    uint32_t value = 5381;
+
+    for (size_t index = 0; index < length; index++) {
+        value = ((value << 5) + value) + start[index];
+    }
+
+    return value;
+}
+
+/**
+ * https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+ */
+static uint32_t
+next_power_of_two(uint32_t v) {
+    // Avoid underflow in subtraction on next line.
+    if (v == 0) {
+        // 1 is the nearest power of 2 to 0 (2^0)
+        return 1;
+    }
+    v--;
+    v |= v >> 1;
+    v |= v >> 2;
+    v |= v >> 4;
+    v |= v >> 8;
+    v |= v >> 16;
+    v++;
+    return v;
+}
+
+#ifndef NDEBUG
+static bool
+is_power_of_two(uint32_t size) {
+    return (size & (size - 1)) == 0;
+}
+#endif
+
+/**
+ * Resize a constant pool to a given capacity.
+ */
+static inline bool
+pm_constant_pool_resize(pm_constant_pool_t *pool) {
+    assert(is_power_of_two(pool->capacity));
+
+    uint32_t next_capacity = pool->capacity * 2;
+    if (next_capacity < pool->capacity) return false;
+
+    const uint32_t mask = next_capacity - 1;
+    const size_t element_size = sizeof(pm_constant_pool_bucket_t) + sizeof(pm_constant_t);
+
+    void *next = xcalloc(next_capacity, element_size);
+    if (next == NULL) return false;
+
+    pm_constant_pool_bucket_t *next_buckets = next;
+    pm_constant_t *next_constants = (void *)(((char *) next) + next_capacity * sizeof(pm_constant_pool_bucket_t));
+
+    // For each bucket in the current constant pool, find the index in the
+    // next constant pool, and insert it.
+    for (uint32_t index = 0; index < pool->capacity; index++) {
+        pm_constant_pool_bucket_t *bucket = &pool->buckets[index];
+
+        // If an id is set on this constant, then we know we have content here.
+        // In this case we need to insert it into the next constant pool.
+        if (bucket->id != PM_CONSTANT_ID_UNSET) {
+            uint32_t next_index = bucket->hash & mask;
+
+            // This implements linear scanning to find the next available slot
+            // in case this index is already taken. We don't need to bother
+            // comparing the values since we know that the hash is unique.
+            while (next_buckets[next_index].id != PM_CONSTANT_ID_UNSET) {
+                next_index = (next_index + 1) & mask;
+            }
+
+            // Here we copy over the entire bucket, which includes the id so
+            // that they are consistent between resizes.
+            next_buckets[next_index] = *bucket;
+        }
+    }
+
+    // The constants are stable with respect to hash table resizes.
+    memcpy(next_constants, pool->constants, pool->size * sizeof(pm_constant_t));
+
+    // pool->constants and pool->buckets are allocated out of the same chunk
+    // of memory, with the buckets coming first.
+    xfree(pool->buckets);
+    pool->constants = next_constants;
+    pool->buckets = next_buckets;
+    pool->capacity = next_capacity;
+    return true;
+}
+
+/**
+ * Initialize a new constant pool with a given capacity.
+ */
+bool
+pm_constant_pool_init(pm_constant_pool_t *pool, uint32_t capacity) {
+    const uint32_t maximum = (~((uint32_t) 0));
+    if (capacity >= ((maximum / 2) + 1)) return false;
+
+    capacity = next_power_of_two(capacity);
+    const size_t element_size = sizeof(pm_constant_pool_bucket_t) + sizeof(pm_constant_t);
+    void *memory = xcalloc(capacity, element_size);
+    if (memory == NULL) return false;
+
+    pool->buckets = memory;
+    pool->constants = (void *)(((char *)memory) + capacity * sizeof(pm_constant_pool_bucket_t));
+    pool->size = 0;
+    pool->capacity = capacity;
+    return true;
+}
+
+/**
+ * Return a pointer to the constant indicated by the given constant id.
+ */
+pm_constant_t *
+pm_constant_pool_id_to_constant(const pm_constant_pool_t *pool, pm_constant_id_t constant_id) {
+    assert(constant_id != PM_CONSTANT_ID_UNSET && constant_id <= pool->size);
+    return &pool->constants[constant_id - 1];
+}
+
+/**
+ * Find a constant in a constant pool. Returns the id of the constant, or 0 if
+ * the constant is not found.
+ */
+pm_constant_id_t
+pm_constant_pool_find(const pm_constant_pool_t *pool, const uint8_t *start, size_t length) {
+    assert(is_power_of_two(pool->capacity));
+    const uint32_t mask = pool->capacity - 1;
+
+    uint32_t hash = pm_constant_pool_hash(start, length);
+    uint32_t index = hash & mask;
+    pm_constant_pool_bucket_t *bucket;
+
+    while (bucket = &pool->buckets[index], bucket->id != PM_CONSTANT_ID_UNSET) {
+        pm_constant_t *constant = &pool->constants[bucket->id - 1];
+        if ((constant->length == length) && memcmp(constant->start, start, length) == 0) {
+            return bucket->id;
+        }
+
+        index = (index + 1) & mask;
+    }
+
+    return PM_CONSTANT_ID_UNSET;
+}
+
+/**
+ * Insert a constant into a constant pool and return its index in the pool.
+ */
+static inline pm_constant_id_t
+pm_constant_pool_insert(pm_constant_pool_t *pool, const uint8_t *start, size_t length, pm_constant_pool_bucket_type_t type) {
+    if (pool->size >= (pool->capacity / 4 * 3)) {
+        if (!pm_constant_pool_resize(pool)) return PM_CONSTANT_ID_UNSET;
+    }
+
+    assert(is_power_of_two(pool->capacity));
+    const uint32_t mask = pool->capacity - 1;
+
+    uint32_t hash = pm_constant_pool_hash(start, length);
+    uint32_t index = hash & mask;
+    pm_constant_pool_bucket_t *bucket;
+
+    while (bucket = &pool->buckets[index], bucket->id != PM_CONSTANT_ID_UNSET) {
+        // If there is a collision, then we need to check if the content is the
+        // same as the content we are trying to insert. If it is, then we can
+        // return the id of the existing constant.
+        pm_constant_t *constant = &pool->constants[bucket->id - 1];
+
+        if ((constant->length == length) && memcmp(constant->start, start, length) == 0) {
+            // Since we have found a match, we need to check if this is
+            // attempting to insert a shared or an owned constant. We want to
+            // prefer shared constants since they don't require allocations.
+            if (type == PM_CONSTANT_POOL_BUCKET_OWNED) {
+                // If we're attempting to insert an owned constant and we have
+                // an existing constant, then either way we don't want the given
+                // memory. Either it's duplicated with the existing constant or
+                // it's not necessary because we have a shared version.
+                xfree((void *) start);
+            } else if (bucket->type == PM_CONSTANT_POOL_BUCKET_OWNED) {
+                // If we're attempting to insert a shared constant and the
+                // existing constant is owned, then we can free the owned
+                // constant and replace it with the shared constant.
+                xfree((void *) constant->start);
+                constant->start = start;
+                bucket->type = (unsigned int) (PM_CONSTANT_POOL_BUCKET_DEFAULT & 0x3);
+            }
+
+            return bucket->id;
+        }
+
+        index = (index + 1) & mask;
+    }
+
+    // IDs are allocated starting at 1, since the value 0 denotes a non-existent
+    // constant.
+    uint32_t id = ++pool->size;
+    assert(pool->size < ((uint32_t) (1 << 30)));
+
+    *bucket = (pm_constant_pool_bucket_t) {
+        .id = (unsigned int) (id & 0x3fffffff),
+        .type = (unsigned int) (type & 0x3),
+        .hash = hash
+    };
+
+    pool->constants[id - 1] = (pm_constant_t) {
+        .start = start,
+        .length = length,
+    };
+
+    return id;
+}
+
+/**
+ * Insert a constant into a constant pool. Returns the id of the constant, or
+ * PM_CONSTANT_ID_UNSET if any potential calls to resize fail.
+ */
+pm_constant_id_t
+pm_constant_pool_insert_shared(pm_constant_pool_t *pool, const uint8_t *start, size_t length) {
+    return pm_constant_pool_insert(pool, start, length, PM_CONSTANT_POOL_BUCKET_DEFAULT);
+}
+
+/**
+ * Insert a constant into a constant pool from memory that is now owned by the
+ * constant pool. Returns the id of the constant, or PM_CONSTANT_ID_UNSET if any
+ * potential calls to resize fail.
+ */
+pm_constant_id_t
+pm_constant_pool_insert_owned(pm_constant_pool_t *pool, uint8_t *start, size_t length) {
+    return pm_constant_pool_insert(pool, start, length, PM_CONSTANT_POOL_BUCKET_OWNED);
+}
+
+/**
+ * Insert a constant into a constant pool from memory that is constant. Returns
+ * the id of the constant, or PM_CONSTANT_ID_UNSET if any potential calls to
+ * resize fail.
+ */
+pm_constant_id_t
+pm_constant_pool_insert_constant(pm_constant_pool_t *pool, const uint8_t *start, size_t length) {
+    return pm_constant_pool_insert(pool, start, length, PM_CONSTANT_POOL_BUCKET_CONSTANT);
+}
+
+/**
+ * Free the memory associated with a constant pool.
+ */
+void
+pm_constant_pool_free(pm_constant_pool_t *pool) {
+    // For each constant in the current constant pool, free the contents if the
+    // contents are owned.
+    for (uint32_t index = 0; index < pool->capacity; index++) {
+        pm_constant_pool_bucket_t *bucket = &pool->buckets[index];
+
+        // If an id is set on this constant, then we know we have content here.
+        if (bucket->id != PM_CONSTANT_ID_UNSET && bucket->type == PM_CONSTANT_POOL_BUCKET_OWNED) {
+            pm_constant_t *constant = &pool->constants[bucket->id - 1];
+            xfree((void *) constant->start);
+        }
+    }
+
+    xfree(pool->buckets);
+}