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cpp interop changes - drop _Bool, use portable popcount and highest_bit_position implementations #14

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Merged
merged 5 commits into from
Dec 28, 2021
Merged

cpp interop changes - drop _Bool, use portable popcount and highest_bit_position implementations #14

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276b036
Replace `_Bool` with `unsigned int` to facilitate interop with cpp co…
spaskalev Dec 28, 2021
060139c
Replace __builtin_popcount with a lookup table implementation, added …
spaskalev Dec 28, 2021
6fa0477
Replace __builtin_clzl with a binary-search-like highest_bit_position…
spaskalev Dec 28, 2021
eb2a9fb
Add an explicit (unsigned char *) cast before calling position_for_ad…
spaskalev Dec 28, 2021
8298efd
Do not import <stdalign.h>
spaskalev Dec 28, 2021
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96 changes: 56 additions & 40 deletions buddy_alloc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,6 @@
#define BUDDY_ALLOC_H

#include <limits.h>
#include <stdalign.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
Expand All @@ -41,10 +40,10 @@ struct buddy *buddy_embed(unsigned char *main, size_t memory_size);
struct buddy *buddy_resize(struct buddy *buddy, size_t new_memory_size);

/* Tests if the allocation can be shrunk in half */
_Bool buddy_can_shrink(struct buddy *buddy);
unsigned int buddy_can_shrink(struct buddy *buddy);

/* Tests if the allocation is completely empty */
_Bool buddy_is_empty(struct buddy *buddy);
unsigned int buddy_is_empty(struct buddy *buddy);

/* Reports the arena size */
size_t buddy_arena_size(struct buddy *buddy);
Expand Down Expand Up @@ -105,7 +104,7 @@ static size_t buddy_tree_sizeof(uint8_t order);
static struct buddy_tree *buddy_tree_init(unsigned char *at, uint8_t order);

/* Indicates whether this is a valid position for the tree */
static _Bool buddy_tree_valid(struct buddy_tree *t, buddy_tree_pos pos);
static unsigned int buddy_tree_valid(struct buddy_tree *t, buddy_tree_pos pos);

/* Returns the order of the specified buddy allocation tree */
static uint8_t buddy_tree_order(struct buddy_tree *t);
Expand Down Expand Up @@ -146,7 +145,7 @@ static size_t buddy_tree_index(buddy_tree_pos pos);
static struct buddy_tree_interval buddy_tree_interval(struct buddy_tree *t, buddy_tree_pos pos);

/* Checks if one interval contains another */
static _Bool buddy_tree_interval_contains(struct buddy_tree_interval outer,
static unsigned int buddy_tree_interval_contains(struct buddy_tree_interval outer,
struct buddy_tree_interval inner);

/*
Expand All @@ -166,10 +165,10 @@ static void buddy_tree_release(struct buddy_tree *t, buddy_tree_pos pos);
static buddy_tree_pos buddy_tree_find_free(struct buddy_tree *t, uint8_t depth);

/* Tests if the incidated position is available for allocation */
static _Bool buddy_tree_is_free(struct buddy_tree *t, buddy_tree_pos pos);
static unsigned int buddy_tree_is_free(struct buddy_tree *t, buddy_tree_pos pos);

/* Tests if the tree can be shrank in half */
static _Bool buddy_tree_can_shrink(struct buddy_tree *t);
static unsigned int buddy_tree_can_shrink(struct buddy_tree *t);

/*
* Debug functions
Expand All @@ -179,7 +178,7 @@ static _Bool buddy_tree_can_shrink(struct buddy_tree *t);
static void buddy_tree_debug(FILE *stream, struct buddy_tree *t, buddy_tree_pos pos, size_t start_size);

/* Implementation defined */
static _Bool buddy_tree_check_invariant(struct buddy_tree *t, buddy_tree_pos pos);
static unsigned int buddy_tree_check_invariant(struct buddy_tree *t, buddy_tree_pos pos);

/*
* A char-backed bitset implementation
Expand All @@ -197,7 +196,7 @@ static inline void bitset_set(unsigned char *bitset, size_t pos);

static inline void bitset_clear(unsigned char *bitset, size_t pos);

static inline _Bool bitset_test(const unsigned char *bitset, size_t pos);
static inline unsigned int bitset_test(const unsigned char *bitset, size_t pos);

static void bitset_shift_left(unsigned char *bitset, size_t from_pos, size_t to_pos, size_t by);

Expand All @@ -214,8 +213,11 @@ static void bitset_debug(FILE *stream, unsigned char *bitset, size_t length);
Bits
*/

/* Returns the number of set bits in the given byte */
static unsigned int popcount_byte(unsigned char b);

/* Returns the index of the highest bit set (1-based) */
static inline size_t highest_bit_position(size_t value);
static size_t highest_bit_position(size_t value);

/* Returns the nearest larger or equal power of two */
static inline size_t ceiling_power_of_two(size_t value);
Expand All @@ -235,12 +237,12 @@ struct buddy {
unsigned char *main;
ptrdiff_t main_offset;
};
_Bool relative_mode;
unsigned int relative_mode;
unsigned char buddy_tree[];
};

struct buddy_embed_check {
_Bool can_fit;
unsigned int can_fit;
size_t offset;
size_t buddy_size;
};
Expand All @@ -252,10 +254,10 @@ static void *address_for_position(struct buddy *buddy, buddy_tree_pos pos);
static buddy_tree_pos position_for_address(struct buddy *buddy, const unsigned char *addr);
static unsigned char *buddy_main(struct buddy *buddy);
static struct buddy_tree *buddy_tree(struct buddy *buddy);
static void buddy_toggle_virtual_slots(struct buddy *buddy, _Bool state);
static void buddy_toggle_virtual_slots(struct buddy *buddy, unsigned int state);
static struct buddy *buddy_resize_standard(struct buddy *buddy, size_t new_memory_size);
static struct buddy *buddy_resize_embedded(struct buddy *buddy, size_t new_memory_size);
static _Bool buddy_is_free(struct buddy *buddy, size_t from);
static unsigned int buddy_is_free(struct buddy *buddy, size_t from);
static struct buddy_embed_check buddy_embed_offset(size_t memory_size);
static buddy_tree_pos deepest_position_for_offset(struct buddy *buddy, size_t offset);

Expand Down Expand Up @@ -383,14 +385,14 @@ static struct buddy *buddy_resize_embedded(struct buddy *buddy, size_t new_memor
return relocated;
}

_Bool buddy_can_shrink(struct buddy *buddy) {
unsigned int buddy_can_shrink(struct buddy *buddy) {
if (buddy == NULL) {
return 0;
}
return buddy_is_free(buddy, buddy->memory_size / 2);
}

_Bool buddy_is_empty(struct buddy *buddy) {
unsigned int buddy_is_empty(struct buddy *buddy) {
if (buddy == NULL) {
return 1;
}
Expand Down Expand Up @@ -482,7 +484,7 @@ void *buddy_realloc(struct buddy *buddy, void *ptr, size_t requested_size) {
}

/* Find the position tracking this address */
buddy_tree_pos origin = position_for_address(buddy, ptr);
buddy_tree_pos origin = position_for_address(buddy, (unsigned char *) ptr);
if (!origin) {
return NULL;
}
Expand Down Expand Up @@ -612,7 +614,7 @@ static unsigned char *buddy_main(struct buddy *buddy) {
return buddy->main;
}

static void buddy_toggle_virtual_slots(struct buddy *buddy, _Bool state) {
static void buddy_toggle_virtual_slots(struct buddy *buddy, unsigned int state) {
size_t memory_size = buddy->memory_size;
/* Mask/unmask the virtual space if memory is not a power of two */
size_t effective_memory_size = ceiling_power_of_two(memory_size);
Expand Down Expand Up @@ -661,7 +663,7 @@ static void buddy_toggle_virtual_slots(struct buddy *buddy, _Bool state) {
/* Internal function that checks if there are any allocations
after the indicated relative memory index. Used to check if
the arena can be downsized. */
static _Bool buddy_is_free(struct buddy *buddy, size_t from) {
static unsigned int buddy_is_free(struct buddy *buddy, size_t from) {
/* from is already adjusted for alignment */

size_t effective_memory_size = ceiling_power_of_two(buddy->memory_size);
Expand Down Expand Up @@ -908,7 +910,7 @@ static void buddy_tree_shrink(struct buddy_tree *t, uint8_t desired_order) {
}
}

static _Bool buddy_tree_valid(struct buddy_tree *t, buddy_tree_pos pos) {
static unsigned int buddy_tree_valid(struct buddy_tree *t, buddy_tree_pos pos) {
return pos && (pos < t->upper_pos_bound);
}

Expand Down Expand Up @@ -1020,7 +1022,7 @@ static struct buddy_tree_interval buddy_tree_interval(struct buddy_tree *t, budd
return result;
}

static _Bool buddy_tree_interval_contains(struct buddy_tree_interval outer,
static unsigned int buddy_tree_interval_contains(struct buddy_tree_interval outer,
struct buddy_tree_interval inner) {
return (inner.from >= outer.from)
&& (inner.from <= outer.to)
Expand Down Expand Up @@ -1139,7 +1141,7 @@ static buddy_tree_pos buddy_tree_find_free(struct buddy_tree *t, uint8_t target_
}
}

static _Bool buddy_tree_is_free(struct buddy_tree *t, buddy_tree_pos pos) {
static unsigned int buddy_tree_is_free(struct buddy_tree *t, buddy_tree_pos pos) {
if (buddy_tree_status(t, pos)) {
return 0;
}
Expand All @@ -1155,7 +1157,7 @@ static _Bool buddy_tree_is_free(struct buddy_tree *t, buddy_tree_pos pos) {
return 1;
}

static _Bool buddy_tree_can_shrink(struct buddy_tree *t) {
static unsigned int buddy_tree_can_shrink(struct buddy_tree *t) {
if (buddy_tree_status(t, buddy_tree_right_child(buddy_tree_root())) != 0) {
return 0; /* Refusing to shrink with right subtree still used! */
}
Expand All @@ -1175,7 +1177,7 @@ static void buddy_tree_debug(FILE *stream, struct buddy_tree *t, buddy_tree_pos
}

buddy_tree_pos start = pos;
_Bool going_up = 0;
unsigned int going_up = 0;
while (1) {
if (going_up) {
if (pos == start) {
Expand Down Expand Up @@ -1215,10 +1217,10 @@ static void buddy_tree_debug(FILE *stream, struct buddy_tree *t, buddy_tree_pos
fflush(stdout);
}

static _Bool buddy_tree_check_invariant(struct buddy_tree *t, buddy_tree_pos pos) {
static unsigned int buddy_tree_check_invariant(struct buddy_tree *t, buddy_tree_pos pos) {
buddy_tree_pos start = pos;
_Bool going_up = 0;
_Bool fail = 0;
unsigned int going_up = 0;
unsigned int fail = 0;
while (1) {
if (going_up) {
if (pos == start) {
Expand All @@ -1239,7 +1241,7 @@ static _Bool buddy_tree_check_invariant(struct buddy_tree *t, buddy_tree_pos pos
size_t left_child_status = buddy_tree_status(t, buddy_tree_left_child(pos));
size_t right_child_status = buddy_tree_status(t, buddy_tree_right_child(pos));

_Bool violated = 0;
unsigned int violated = 0;

if (left_child_status || right_child_status) {
size_t min = left_child_status <= right_child_status
Expand Down Expand Up @@ -1291,13 +1293,13 @@ static inline void bitset_clear(unsigned char *bitset, size_t pos) {
bitset[bucket] &= ~bitset_index_mask[index];
}

static inline _Bool bitset_test(const unsigned char *bitset, size_t pos) {
static inline unsigned int bitset_test(const unsigned char *bitset, size_t pos) {
size_t bucket = pos / CHAR_BIT;
size_t index = pos % CHAR_BIT;
return bitset[bucket] & bitset_index_mask[index];
}

static uint8_t bitset_char_mask[8][8] = {
static const uint8_t bitset_char_mask[8][8] = {
{1, 3, 7, 15, 31, 63, 127, 255},
{0, 2, 6, 14, 30, 62, 126, 254},
{0, 0, 4, 12, 28, 60, 124, 252},
Expand Down Expand Up @@ -1352,13 +1354,13 @@ static size_t bitset_count_range(unsigned char *bitset, size_t from_pos, size_t
size_t to_index = to_pos % CHAR_BIT;

if (from_bucket == to_bucket) {
return __builtin_popcount(bitset[from_bucket] & bitset_char_mask[from_index][to_index]);
return popcount_byte(bitset[from_bucket] & bitset_char_mask[from_index][to_index]);
}

size_t result = __builtin_popcount(bitset[from_bucket] & bitset_char_mask[from_index][7])
+ __builtin_popcount(bitset[to_bucket] & bitset_char_mask[0][to_index]);
size_t result = popcount_byte(bitset[from_bucket] & bitset_char_mask[from_index][7])
+ popcount_byte(bitset[to_bucket] & bitset_char_mask[0][to_index]);
while(++from_bucket != to_bucket) {
result += __builtin_popcount(bitset[from_bucket]);
result += popcount_byte(bitset[from_bucket]);
}
return result;
}
Expand Down Expand Up @@ -1393,23 +1395,37 @@ static void bitset_shift_right(unsigned char *bitset, size_t from_pos, size_t to

static void bitset_debug(FILE *stream, unsigned char *bitset, size_t length) {
for (size_t i = 0; i < length; i++) {
fprintf(stream, "%zu: %d\n", i, bitset_test(bitset, i));
fprintf(stream, "%zu: %d\n", i, bitset_test(bitset, i) && 1);
}
}

/*
Bits
*/

/* Returns the higest set bit position for the given value. Do not call with zero. */
static inline size_t highest_bit_position(size_t value) {
assert(value);
return ((sizeof(size_t) * CHAR_BIT) - __builtin_clzl(value));
static const unsigned char popcount_lookup[16] = {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};

static unsigned int popcount_byte(unsigned char b) {
return popcount_lookup[b & 15] + popcount_lookup[b >> 4];
}

/* Returns the higest set bit position for the given value. Returns zero for zero. */
static size_t highest_bit_position(size_t value) {
int result = 0;
const size_t all_set[] = {4294967295, 65535, 255, 15, 7, 3, 1};
const size_t count[] = {32, 16, 8, 4, 2, 1, 1};
for (size_t i = 0; i < 7; i++) {
if (value >= all_set[i]) {
value >>= count[i];
result += count[i];
}
}
return result + value;
}

static inline size_t ceiling_power_of_two(size_t value) {
value += !value; /* branchless x -> { 1 for 0, x for x } */
return 1u << ((sizeof(size_t) * CHAR_BIT) - __builtin_clzl(value + value - 1)-1);
return 1u << (highest_bit_position(value + value - 1)-1);
}

#endif /* BUDDY_ALLOC_IMPLEMENTATION */
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