114 lines
2.6 KiB
C
114 lines
2.6 KiB
C
#include <stdint.h>
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#include "assert.h"
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#include "printf.h"
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#define block_power (5UL)
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#define block_size (1UL << block_power)
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//static uint8_t memory[0x100];
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static uint8_t memory[0x100000];
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#define free_list_length ((sizeof (memory)) / block_size)
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static uint8_t free_list[free_list_length];
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static uint32_t free_ix;
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void memory_reset_free_list()
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{
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for (int i = 0; i < (sizeof (free_list)); i++) {
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free_list[i] = 0;
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}
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free_ix = 0;
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}
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static inline uint32_t find_contiguous_blocks(uint32_t blocks, int * zero_crossing)
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{
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if (free_ix + blocks > free_list_length) {
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free_ix = 0; // non-contiguous
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(*zero_crossing) += 1;
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}
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for (uint32_t i = 0; i < blocks; i++) {
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if (free_list[free_ix + i] != 0)
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return i + 1;
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}
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return blocks;
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}
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void * memory_allocate(uint32_t size)
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{
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assert(size != 0);
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uint32_t blocks = ((size + (block_size - 1)) & ~(block_size - 1)) >> block_power;
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int zero_crossings = 0;
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while (true) {
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uint32_t ix_offset = find_contiguous_blocks(blocks, &zero_crossings);
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if (zero_crossings > 1)
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return nullptr; // memory allocation failed
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if (ix_offset == blocks)
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break;
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free_ix = (free_ix + ix_offset) & (free_list_length - 1);
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}
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for (int i = 0; i < (blocks - 1); i++) {
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free_list[free_ix + i] = 2;
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}
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free_list[free_ix + (blocks - 1)] = 1;
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void * mem = &memory[free_ix << block_power];
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free_ix = (free_ix + blocks) & (free_list_length - 1);
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return mem;
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}
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void memory_free(void * p)
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{
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assert(((uint8_t*)p) >= memory);
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uint32_t offset = (((uint8_t*)p) - memory) >> block_power;
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assert(free_list[offset] != 0);
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while (free_list[offset] == 2) {
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free_list[offset] = 0;
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offset += 1;
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}
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assert(free_list[offset] == 1);
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free_list[offset] = 0;
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}
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#if 0
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int main()
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{
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memory_reset_free_list();
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printf("%p\n", memory);
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void * p1 = memory_allocate(32);
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printf("p1 %p\n", p1);
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void * p2 = memory_allocate(16);
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printf("p2 %p\n", p2);
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void * p3 = memory_allocate(256);
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printf("p3 %p\n", p3);
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void * p4 = memory_allocate(90);
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printf("p4 %p\n", p4);
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for (int i = 0; i < free_list_length; i++) { printf("%d ", free_list[i]); }
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printf("\n");
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memory_free(p2);
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memory_free(p1);
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void * p5 = memory_allocate(256);
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printf("%p\n", p4);
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for (int i = 0; i < free_list_length; i++) { printf("%d ", free_list[i]); }
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printf("\n");
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void * p6 = memory_allocate(128);
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printf("p5 %p\n", p5);
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memory_free(p4);
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void * p7 = memory_allocate(128);
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printf("p6 %p\n", p6);
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void * p8 = memory_allocate(128);
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printf("p7 %p\n", p7);
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void * p9 = memory_allocate(128);
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printf("p8 %p\n", p8);
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}
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#endif
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