Added the ability to disable the prefix byte.

Any instructions that either have a register size of
8 bits, use implied addressing, or branch can save a
byte by disabling the prefix byte.

It does this by checking if the first three bits are
all set to 1.
If true, then it will treat it as a prefix
byte, otherwise, it will treat it as an opcode.

1 files changed, 20 insertions, 6 deletions

diff --git a/sux.c b/sux.c
index f42c0da..7bb8661 100644
--- a/sux.c
+++ b/sux.c
@@ -6,7 +6,8 @@
 
 int run(struct sux *cpu, uint8_t prefix, uint8_t opcode, uint8_t thread) {
 	uint64_t address;
-	uint8_t regsize = (1 << (prefix & 3));
+	uint8_t rs = (prefix & 0x30) >> 4;
+	uint8_t regsize = (1 << rs);
 	uint8_t tmp;
 	address = cpu->pc[thread];
 #if !bench
@@ -17,7 +18,10 @@ int run(struct sux *cpu, uint8_t prefix, uint8_t opcode, uint8_t thread) {
 	fflush(stdout);
 #endif
 	cpu->pc[thread]++;
-	clk++;
+	if (ibcount > 8) {
+		clk++;
+		ibcount = 0;
+	}
 	switch(opcode) {
 		case CPS: /* Clear Processor Status. */
 			for (uint8_t i = 0; i < 8; i++) {
@@ -366,6 +370,7 @@ int main(int argc, char **argv) {
 	cpu.x[0] = 0;
 	cpu.y[0] = 0;
 	cpu.sp = 0xFFFF;
+	ibcount = 0;
 	addr = malloc(8*0x04000000);
 	int v = 0;
 	if (asmmon() == 2)
@@ -416,13 +421,21 @@ int main(int argc, char **argv) {
 	st = clock();
 #endif
 	while (!end) {
-		prefix = addr[cpu.pc[0]++];
+		prefix = addr[cpu.pc[0]];
+		if ((prefix & 0x07) == 0x07) {
+			cpu.pc[0]++;
+			ibcount++;
+		}
 		opcode = addr[cpu.pc[0]];
+		ibcount++;
 #if !bench
 		printf("\033[%uH\033[2K", lines);
 		lines++;
 #endif
-		run(&cpu, prefix, opcode, 0);
+		if ((prefix & 0x07) == 0x07)
+			run(&cpu, prefix-7, opcode, 0);
+		else
+			run(&cpu, 0, opcode, 0);
 #if !bench
 		if (lines > 24)
 			lines = 2;
@@ -431,9 +444,8 @@ int main(int argc, char **argv) {
 		t0 = ((double)clock() - (double)st)/(double)CLOCKS_PER_SEC;
 #endif
 		inst++;
-
 #if !bench
-		printf("\033[HInstructions executed: %llu, Clock cycles: %llu\n", inst, clk);
+		printf("\033[HInstruction bytes: %x, Instructions executed: %llu, Clock cycles: %llu\n", ibcount, inst, clk);
 		fflush(stdout);
 #endif
 #if bench
@@ -441,6 +453,8 @@ int main(int argc, char **argv) {
 			end = 1;
 		}
 #endif
+		if (ibcount >= 7)
+			ibcount = 0;
 	}
 #if bench
 	en = (double)clock();