ra8_stbtt_alloc.c

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#include "ra8_stbtt_alloc.h"
 
#include <stdalign.h>
#include <stddef.h>
#include <stdint.h>

typedef enum : uint32_t {
  k_ra8_stbtt_align       = 16U,         
  k_ra8_stbtt_align_mask  = 15U,         
  k_ra8_stbtt_arena_bytes = 96U * 1024U, 
} ra8_stbtt_alloc_consts_t;

alignas(k_ra8_stbtt_align) static uint8_t s_arena[k_ra8_stbtt_arena_bytes];

static size_t s_offset = 0U;

static size_t s_live = 0U;

static size_t s_high_water = 0U;
 
void* ra8_stbtt_malloc(size_t n)
{
  /* Reject requests too large to ever fit; this also prevents the
   * alignment round-up below from overflowing. */
  if (n > (size_t)k_ra8_stbtt_arena_bytes) {
    return nullptr;
  }
  const size_t aligned = (n + (size_t)k_ra8_stbtt_align_mask) & ~(size_t)k_ra8_stbtt_align_mask;
  if (aligned > (size_t)k_ra8_stbtt_arena_bytes - s_offset) {
    return nullptr;
  }
  void* const block = &s_arena[s_offset];
  s_offset += aligned;
  s_live += 1U;
  if (s_offset > s_high_water) {
    s_high_water = s_offset;
  }
  return block;
}
 
void ra8_stbtt_free(void* p)
{
  if (p == nullptr) {
    return;
  }
  if (s_live > 0U) {
    s_live -= 1U;
  }
  if (s_live == 0U) {
    s_offset = 0U;
  }
}
 
size_t ra8_stbtt_alloc_high_water(void)
{
  return s_high_water;
}