nqdasm: Add disassembler

1 files changed, 43 insertions, 0 deletions

diff --git a/nqdasm.c b/nqdasm.c
new file mode 100644
index 0000000..4969f47
--- /dev/null
+++ b/nqdasm.c
@@ -0,0 +1,43 @@
+#include <stdio.h>
+
+#include "mnemonics.h"
+
+static const struct mnemonic *match_instruction(unsigned bits)
+{
+	for (int i = 0; i < MNEM_LAST; i++) {
+		const struct mnemonic *m = mnemonics + i;
+		if ((bits & m->mask) == m->bits) return m;
+	}
+	return NULL;
+}
+
+static void print_operand(unsigned bits, const struct operand *op)
+{
+	switch (op->type) {
+	case REG:    printf( "r%d",      7 & (bits >> op->shift)); break;
+	case REGPTR: printf("@r%d",      7 & (bits >> op->shift)); break;
+	case IMM:    printf(  "%d", (uint8_t)(bits >> op->shift)); break;
+	case PCOFF:  printf(  "%d",  (int8_t)(bits >> op->shift)); break;
+	}
+}
+
+int main()
+{
+	unsigned bits;
+	while (scanf(" %x\n", &bits) > 0) {
+		const struct mnemonic *m = match_instruction(bits);
+		if (!m) {
+			fprintf(stderr, "could not decode instruction 0x%04x\n", bits);
+			continue;
+		}
+
+		printf("\t%s", m->mnem);
+		for (int i = 0; i < 3 && m->operands[i].type; i++) {
+			printf("%s", i ? ", " : " ");
+			print_operand(bits, m->operands + i);
+		}
+		printf("\n");
+	}
+	return 0;
+}
+