feat: support RetroArch's new cheat format (#795)

workspace/all/minarch/ma_cheats.c

@@ -13,12 +13,6 @@ struct Cheats cheatcodes;
 #define CHEAT_MAX_LINE_LEN 52
 #define CHEAT_MAX_LINES    3
 
-static size_t parse_count(FILE *file) {
-	size_t count = 0;
-	fscanf(file, " cheats = %lu\n", (unsigned long *)&count);
-	return count;
-}
-
 static const char *find_val(const char *start) {
 	start--;
 	while(!isspace(*++start))
@@ -33,9 +27,36 @@ static const char *find_val(const char *start) {
 	while(isspace(*++start))
 		;
 
+	// newer cheat files quote every value, older ones quote only strings
+	if (*start == '"')
+		start++;
+
 	return start;
 }
 
+// the count sits on the first line in older cheat files and on the last line in
+// newer ones, so scan the whole file and keep the last match
+static size_t parse_count(FILE *file) {
+	char line[512];
+	size_t count = 0;
+
+	while (fgets(line, sizeof(line), file)) {
+		const char *ptr = line;
+		while (isspace(*ptr))
+			ptr++;
+
+		// anchored, so a description mentioning "cheats = " can't hijack us
+		if (strncmp(ptr, "cheats", 6))
+			continue;
+
+		if ((ptr = find_val(ptr)))
+			count = strtoul(ptr, NULL, 10);
+	}
+
+	rewind(file);
+	return count;
+}
+
 static int parse_bool(const char *ptr, int *out) {
 	if (!strncasecmp(ptr, "true", 4)) {
 		*out = 1;
@@ -53,9 +74,7 @@ static int parse_string(const char *ptr, char *buf, size_t len) {
 
 	buf[0] = '\0';
 
-	if (*ptr++ != '"')
-		return -1;
-
+	// find_val already consumed the opening quote; the closing one is checked below
 	while (*ptr != '\0' && *ptr != '"' && index < len - 1) {
 		if (*ptr == '\\' && index < input_len - 1) {
 			ptr++;
@@ -100,10 +119,14 @@ static int parse_cheats(struct Cheats *cheats, FILE *file) {
 			size_t len;
 			sscanf(ptr, "cheat%d", &index);
 
-			if (index >= cheats->count)
+			if (index < 0 || (size_t)index >= cheats->count)
 				continue;
 			cheat = &cheats->cheats[index];
 
+			// these would otherwise match the _value and _address tests below
+			if (strstr(ptr, "_rumble") || strstr(ptr, "_repeat"))
+				continue;
+
 			if (strstr(ptr, "_desc")) {
 				ptr = find_val(ptr);
 				if (!ptr || parse_string(ptr, buf, sizeof(buf))) {
@@ -153,6 +176,27 @@ static int parse_cheats(struct Cheats *cheats, FILE *file) {
 					continue;
 				}
 			}
+			// the rest describe a memory write, see Cheats_apply
+			// note: _address_bit_position must be tested before _address
+			else if (strstr(ptr, "_address_bit_position")) {
+				if ((ptr = find_val(ptr)))
+					cheat->bit_position = strtoul(ptr, NULL, 10);
+			} else if (strstr(ptr, "_address")) {
+				if ((ptr = find_val(ptr)))
+					cheat->address = strtoul(ptr, NULL, 10);
+			} else if (strstr(ptr, "_value")) {
+				if ((ptr = find_val(ptr)))
+					cheat->value = strtoul(ptr, NULL, 10);
+			} else if (strstr(ptr, "_cheat_type")) {
+				if ((ptr = find_val(ptr)))
+					cheat->type = strtoul(ptr, NULL, 10);
+			} else if (strstr(ptr, "_memory_search_size")) {
+				if ((ptr = find_val(ptr)))
+					cheat->size = strtoul(ptr, NULL, 10);
+			} else if (strstr(ptr, "_big_endian")) {
+				if ((ptr = find_val(ptr)))
+					parse_bool(ptr, &cheat->big_endian);
+			}
 		}
 	} while(1);
 
@@ -249,7 +293,7 @@ void Cheat_getPaths(char paths[CHEAT_MAX_PATHS][MAX_PATH], int* count) {
 
 void Cheats_free() {
 	size_t i;
-	for (i = 0; i < cheatcodes.count; i++) {
+	for (i = 0; cheatcodes.cheats && i < cheatcodes.count; i++) {
 		struct Cheat *cheat = &cheatcodes.cheats[i];
 		if (cheat) {
 			free((char *)cheat->name);
@@ -258,6 +302,7 @@ void Cheats_free() {
 		}
 	}
 	free(cheatcodes.cheats);
+	cheatcodes.cheats = NULL;
 	cheatcodes.count = 0;
 }
 
@@ -320,7 +365,7 @@ bool Cheats_load() {
 	}
 
 	cheatcodes.count = parse_count(file);
-	if (cheatcodes.count <= 0) {
+	if (cheatcodes.count == 0 || cheatcodes.count > CHEAT_MAX_COUNT) {
 		LOG_error("Couldn't read cheat count\n");
 		goto finish;
 	}
@@ -336,7 +381,9 @@ bool Cheats_load() {
 		goto finish;
 	}
 
-	LOG_info("Found %i cheats for the current game.\n", cheatcodes.count);
+	// memory-write cheats are useless without system ram, so report what we got
+	LOG_info("Found %i cheats for the current game (system ram: %zu bytes).\n",
+		cheatcodes.count, core.get_memory_size ? core.get_memory_size(RETRO_MEMORY_SYSTEM_RAM) : 0);
 
 	success = 1;
 finish:
@@ -346,4 +393,58 @@ bool Cheats_load() {
 
 	if (file)
 		fclose(file);
+
+	return success;
+}
+
+// Cheats from RetroArch's newer format carry no code for the core to interpret,
+// they name a memory location to hold at a value. Those have to be rewritten
+// every frame, otherwise the game just overwrites them again.
+// Addresses are treated as offsets into system RAM; cores that publish a memory
+// map (RETRO_ENVIRONMENT_SET_MEMORY_MAPS) may expect a different layout.
+void Cheats_apply(void) {
+	static const unsigned char widths[] = { 0, 0, 0, 1, 2, 4 }; // by memory_search_size
+	unsigned char *ram;
+	size_t ram_size, i;
+
+	if (!core.get_memory_data || !core.get_memory_size)
+		return;
+
+	ram_size = core.get_memory_size(RETRO_MEMORY_SYSTEM_RAM);
+	ram = core.get_memory_data(RETRO_MEMORY_SYSTEM_RAM);
+	if (!ram || !ram_size)
+		return;
+
+	for (i = 0; i < cheatcodes.count; i++) {
+		const struct Cheat *cheat = &cheatcodes.cheats[i];
+		unsigned char width;
+		unsigned value;
+		int shift;
+
+		// code means the core applies it, see Core_applyCheats
+		if (!cheat->enabled || cheat->code || cheat->type != CHEAT_TYPE_SET_TO_VALUE)
+			continue;
+
+		if (cheat->size < 3) {
+			// sub-byte cheat: mask into the byte at bit_position
+			unsigned char mask = (1 << (1 << cheat->size)) - 1;
+			if (cheat->address >= ram_size || cheat->bit_position > 7)
+				continue;
+
+			shift = cheat->bit_position;
+			ram[cheat->address] = (ram[cheat->address] & ~(mask << shift)) | ((cheat->value & mask) << shift);
+			continue;
+		}
+
+		// written this way round so address + width can't overflow
+		width = cheat->size < sizeof(widths) ? widths[cheat->size] : 0;
+		if (!width || width > ram_size || cheat->address > ram_size - width)
+			continue;
+
+		value = cheat->value;
+		for (shift = 0; shift < width; shift++) {
+			int byte = cheat->big_endian ? width - 1 - shift : shift;
+			ram[cheat->address + byte] = (value >> (shift * 8)) & 0xff;
+		}
+	}
 }

workspace/all/minarch/ma_cheats.h

@@ -5,6 +5,8 @@
 
 #include "defines.h"
 
+#define CHEAT_TYPE_SET_TO_VALUE 1
+#define CHEAT_MAX_COUNT         4096
 #define CHEAT_MAX_PATHS         48
 #define CHEAT_MAX_DISPLAY_PATHS 8
 #define CHEAT_MAX_LIST_LENGTH   (CHEAT_MAX_DISPLAY_PATHS * MAX_PATH)
@@ -13,7 +15,16 @@ struct Cheat {
 	const char *name;
 	const char *info;
 	int enabled;
-	const char *code;
+	const char *code; // classic format, handed to retro_cheat_set()
+
+	// RetroArch's newer format describes cheats as a memory write instead of a
+	// code string (handler = 1). Those have no code and are applied by us.
+	unsigned address;
+	unsigned value;
+	unsigned char type;         // cheat_type, 1 = set to value (the only one we apply)
+	unsigned char size;         // memory_search_size, 0-5 = 1,2,4,8,16,32 bits
+	unsigned char bit_position; // address_bit_position, sub-byte sizes only
+	int big_endian;
 };
 
 struct Cheats {
@@ -27,3 +38,4 @@ extern struct Cheats cheatcodes;
 void Cheat_getPaths(char paths[CHEAT_MAX_PATHS][MAX_PATH], int* count);
 void Cheats_free(void);
 bool Cheats_load(void);
+void Cheats_apply(void);

workspace/all/minarch/ma_core.c

@@ -104,7 +104,8 @@ void Core_applyCheats(struct Cheats *cheats)
 
 	core.cheat_reset();
 	for (int i = 0; i < cheats->count; i++) {
-		if (cheats->cheats[i].enabled) {
+		// no code means it describes a memory write, applied by Cheats_apply
+		if (cheats->cheats[i].enabled && cheats->cheats[i].code) {
 			core.cheat_set(i, cheats->cheats[i].enabled, cheats->cheats[i].code);
 		}
 	}

workspace/all/minarch/ma_runframe.c

@@ -1,5 +1,6 @@
 #include <SDL2/SDL.h>
 #include "ma_internal.h"
+#include "ma_cheats.h"
 #include "ma_rewind.h"
 #include "ma_input.h"
 #include "ma_config.h"
@@ -46,6 +47,8 @@ static void limitFF(void) {
 }
 
 void run_frame(void) {
+	Cheats_apply();
+
 	// if rewind is toggled, fast-forward toggle must stay off; fast-forward hold pauses rewind
 	int do_rewind = (rewind_pressed || rewind_toggle) && !(rewind_toggle && ff_hold_active);
 	if (do_rewind) {