MeirGavish
50 lines
1.8 KiB
C
50 lines
1.8 KiB
C
#include "pool.h"
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#include "util.h"
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void pool_bm_clear_idx(PoolBitmap *bm, int idx)
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{
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uint32_t i = idx / POOL_BITS_PER_WORD;
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uint32_t b = idx % POOL_BITS_PER_WORD;
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// Below are the "fast" forms of the above operations, respectively.
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// These are more efficient, but removed for readability
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// See: https://github.com/cellos51/balatro-gba/pull/132#discussion_r2365966071
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// Divide by 32 to get the word index
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//uint32_t i = idx >> 5;
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// Get last 5-bits, same as a modulo (% 32) operation on positive numbers
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//uint32_t b = idx & 0x1F;
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bm->w[i] &= ~((uint32_t)1 << b);
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}
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int pool_bm_get_free_idx(PoolBitmap *bm)
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{
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for (uint32_t i = 0; i < bm->nwords; i++)
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{
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uint32_t inv = ~bm->w[i];
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// guard so we don't call `ctz` with 0, since __builtin_ctz(0) is undefined
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// https://gcc.gnu.org/onlinedocs/gcc/Bit-Operation-Builtins.html#index-_005f_005fbuiltin_005fctz
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//
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// By using the bitwise inverse of the word, you can skip words that are full
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// quickly (where the value is 0 or 'false' since all bits are '1', or 'in use'). Any value greater
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// than 0 indicates there is a free slot. Then, when counting the trailing 0's, you can test very quickly
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// where the first free slot is. This operation prevents looping through every bit of filled flags, and
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// will instead operate only on the first word with free slots.
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if (inv)
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{
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int bit = __builtin_ctz(inv);
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bm->w[i] |= ((uint32_t)1 << bit);
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int idx = i * POOL_BITS_PER_WORD + bit;
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return (idx < bm->cap) ? idx : UNDEFINED;
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}
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}
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return UNDEFINED;
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}
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#define POOL_ENTRY(name, capacity) \
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POOL_DEFINE_TYPE(name, capacity);
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#include POOLS_DEF_FILE
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#undef POOL_ENTRY
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