gb6/system6/cache.c

#include <stdint.h>
#include <stddef.h>
#include <string.h>

#include "types.h"
#include "cache.h"
#include "arena.h"

static void **bank0_cache;
static void **upper_cache;
static void ***banked_cache;

// per-page source byte bounds of compiled upper code (pages 0x80-0xff);
// lo > hi means the page holds no compiled code
static u8 upper_page_lo[0x80];
static u8 upper_page_hi[0x80];

// how many pages back the earliest block covering this page starts
static u8 upper_page_reach[0x80];

#define HRAM_PAGE 0x7f // page $ff in the upper_page_* arrays

static const u8 *hram_page;
static u8 hram_snapshot[0x80];
static u8 hram_is_code[0x80];
static int hram_has_code;

// compiled HRAM source bytes still match what the game is executing?
static int hram_snapshot_valid(void)
{
    int lo = upper_page_lo[HRAM_PAGE];
    int hi = upper_page_hi[HRAM_PAGE];
    int k;

    if (lo < 0x80) {
        lo = 0x80;
    }
    for (k = lo - 0x80; k <= hi - 0x80; k++) {
        if (hram_is_code[k] && hram_page[k] != hram_snapshot[k]) {
            return 0;
        }
    }
    return 1;
}

// Look up cached code pointer for given PC and bank
void *cache_lookup(u16 pc, u8 bank)
{
    if (pc < 0x4000) {
        if (!bank0_cache) {
            return NULL;
        }
        return bank0_cache[pc];
    }
    if (pc < 0x8000) {
        if (!banked_cache || !banked_cache[bank]) {
            return NULL;
        }
        return banked_cache[bank][pc - 0x4000];
    }
    if (!upper_cache) {
        return NULL;
    }
    if (pc >= 0xff80 && hram_has_code && !hram_snapshot_valid()) {
        cache_invalidate_upper_page(0xff);
        return NULL;
    }
    return upper_cache[pc - 0x8000];
}

void cache_set_hram(const u8 *hram)
{
    hram_page = hram;
}

// Store code pointer in cache for given PC and bank
int cache_store(u16 pc, u8 bank, void *code)
{
    if (pc < 0x4000) {
        bank0_cache[pc] = code;
    } else if (pc < 0x8000) {
        if (!banked_cache[bank]) {
            banked_cache[bank] = arena_alloc(BANKED_CACHE_SIZE * sizeof(void *));
            if (!banked_cache[bank]) {
                return 0;
            }
            memset(banked_cache[bank], 0, BANKED_CACHE_SIZE * sizeof(void *));
        }
        banked_cache[bank][pc - 0x4000] = code;
    } else {
        upper_cache[pc - 0x8000] = code;
    }
    return 1;
}

void cache_mark_upper_range(u16 start, u16 end)
{
    int p;
    for (p = (start >> 8); p <= (end >> 8); p++) {
        int idx = p - 0x80;
        if (idx < 0) {
            continue;
        }
        u8 lo = (p == (start >> 8)) ? (start & 0xff) : 0;
        u8 hi = (p == (end >> 8)) ? (end & 0xff) : 0xff;
        if (lo < upper_page_lo[idx]) {
            upper_page_lo[idx] = lo;
        }
        if (hi > upper_page_hi[idx]) {
            upper_page_hi[idx] = hi;
        }
        if (p - (start >> 8) > upper_page_reach[idx]) {
            upper_page_reach[idx] = p - (start >> 8);
        }
    }

    // re-snapshot whenever HRAM gets compiled code
    if (end >= 0xff80 && hram_page) {
        u16 a = start < 0xff80 ? 0xff80 : start;

        for (; a <= end; a++) {
            hram_is_code[a - 0xff80] = 1;
        }
        memcpy(hram_snapshot, hram_page, sizeof hram_snapshot);
        hram_has_code = 1;
    }
}

int cache_upper_range_hit(u16 addr)
{
    int idx = (addr >> 8) - 0x80;
    u8 off = addr & 0xff;
    return off >= upper_page_lo[idx] && off <= upper_page_hi[idx];
}

// any compiled code left anywhere in addr's 4K memory page?
int cache_upper_4k_has_code(u16 addr)
{
    int base = ((addr >> 8) & ~0xf) - 0x80;
    int k;

    for (k = 0; k < 16; k++) {
        if (upper_page_lo[base + k] <= upper_page_hi[base + k]) {
            return 1;
        }
    }
    return 0;
}

void cache_invalidate_upper_page(u8 page)
{
    int idx = page - 0x80;
    int first = idx;
    int k;

    // widen until no block starting before "first" reaches into the range
    for (k = idx; k >= first; k--) {
        int start = k - upper_page_reach[k];
        if (start < first) {
            first = start;
        }
    }

    memset(&upper_cache[first << 8], 0,
            ((idx - first + 1) << 8) * sizeof(void *));
    for (k = first; k <= idx; k++) {
        upper_page_lo[k] = 0xff;
        upper_page_hi[k] = 0;
        upper_page_reach[k] = 0;
    }
    if (idx == HRAM_PAGE) {
        memset(hram_is_code, 0, sizeof hram_is_code);
        hram_has_code = 0;
    }
}

// Allocate and zero all cache arrays upfront
// Returns 1 on success, 0 on failure
int cache_init(void)
{
    memset(upper_page_lo, 0xff, sizeof upper_page_lo);
    memset(upper_page_hi, 0, sizeof upper_page_hi);
    memset(upper_page_reach, 0, sizeof upper_page_reach);
    memset(hram_is_code, 0, sizeof hram_is_code);
    hram_has_code = 0;

    bank0_cache = arena_alloc(BANK0_CACHE_SIZE * sizeof(void *));
    if (!bank0_cache) {
        return 0;
    }
    memset(bank0_cache, 0, BANK0_CACHE_SIZE * sizeof(void *));

    upper_cache = arena_alloc(UPPER_CACHE_SIZE * sizeof(void *));
    if (!upper_cache) {
        return 0;
    }
    memset(upper_cache, 0, UPPER_CACHE_SIZE * sizeof(void *));

    // Just the array of bank pointers, not each bank's cache
    banked_cache = arena_alloc(MAX_ROM_BANKS * sizeof(void **));
    if (!banked_cache) {
        return 0;
    }
    memset(banked_cache, 0, MAX_ROM_BANKS * sizeof(void **));

    return 1;
}

void cache_shutdown(void)
{
    bank0_cache = NULL;
    upper_cache = NULL;
    banked_cache = NULL;
}

// Get current cache array pointers for dispatcher
void cache_get_arrays(void ***out_bank0, void ****out_banked, void ***out_upper)
{
    *out_bank0 = bank0_cache;
    *out_banked = banked_cache;
    *out_upper = upper_cache;
}