nqdasm: use a static buffer for input lines

Simplifies buffer handling and searches for lines by address.

1 files changed, 33 insertions, 65 deletions

diff --git a/nqdasm.c b/nqdasm.c
index d7016fb..5449c06 100644
--- a/nqdasm.c
+++ b/nqdasm.c
@@ -24,12 +24,15 @@ const char *progname;
 		perror(str); \
 	} while (0)
 
-struct line {
+static struct line {
 	const struct mnemonic *mnem;
-	uint16_t addr;
 	uint16_t value;
 	int      label;
-};
+} lines[0x7fff];
+
+static size_t maxpc;
+
+#define LINE(addr)  &lines[(uint16_t)(addr) >> 1]
 
 static const struct mnemonic *match_instruction(unsigned bits)
 {
@@ -52,29 +55,23 @@ static inline int get_argvalue(const struct line *line, int argidx)
 	assert(0);
 }
 
-static int cmp_line_addr(const void *a, const void *b)
-{
-	const struct line *la = (const struct line*)a;
-	const struct line *lb = (const struct line*)b;
-	return la->addr < lb->addr ? -1 : la->addr == lb->addr ? 0 : 1;
-}
-
-static struct line *get_pcoff_target(const struct line *lines, size_t count, const struct line *inst, int argidx)
+static struct line *get_pcoff_target(uint16_t pc, int argidx)
 {
-	uint16_t targetaddr = inst->addr + get_argvalue(inst, argidx);
-	return bsearch(&(struct line){ .addr = targetaddr }, lines, count, sizeof *lines, cmp_line_addr);
+	struct line *l = LINE(pc + get_argvalue(LINE(pc), argidx));
+	return l - lines >= 2*maxpc ? NULL : l;
 }
 
-static void assign_labels(struct line *lines, size_t count)
+static void assign_labels(void)
 {
 	/* mark those addresses that need a label */
-	for (size_t i = 0; i < count; i++) {
-		if (!lines[i].mnem) continue;
+	for (size_t pc = 0; pc < maxpc; pc += 2) {
+		const struct line *l = LINE(pc);
+		if (!l->mnem) continue;
 
-		const struct operand *ops = lines[i].mnem->operands;
+		const struct operand *ops = l->mnem->operands;
 		for (int j = 0; j < 3 && ops[j].type; j++) {
 			if (ops[j].type == PCOFF) {
-				struct line *target = get_pcoff_target(lines, count, lines + i, j);
+				struct line *target = get_pcoff_target(pc, j);
 				if (target) target->label = 1;
 			}
 		}
@@ -82,14 +79,15 @@ static void assign_labels(struct line *lines, size_t count)
 
 	/* assign labels in ascending order */
 	int label = 0;
-	for (size_t i = 0; i < count; i++) {
-		lines[i].label = lines[i].label ? label++ : -1;
+	for (size_t pc = 0; pc < maxpc; pc += 2) {
+		struct line *l = LINE(pc);
+		l->label = l->label ? label++ : -1;
 	}
 }
 
-static void print_operand(FILE *out, const struct line *lines, size_t count, size_t lineidx, size_t argidx)
+static void print_operand(FILE *out, size_t pc, size_t argidx)
 {
-	const struct line  *inst = lines + lineidx;
+	const struct line  *inst = LINE(pc);
 	const struct operand *op = inst->mnem->operands + argidx;
 
 	switch (op->type) {
@@ -97,7 +95,7 @@ static void print_operand(FILE *out, const struct line *lines, size_t count, siz
 	case REGPTR: fprintf(out, "@r%d", get_argvalue(inst, argidx)); break;
 	case IMM:    fprintf(out,   "%d", get_argvalue(inst, argidx)); break;
 	case PCOFF: {
-			const struct line *target = get_pcoff_target(lines, count, inst, argidx);
+			const struct line *target = get_pcoff_target(pc, argidx);
 			if (target && target->label >= 0)
 				fprintf(out, "L%d", target->label);
 			else
@@ -108,59 +106,31 @@ static void print_operand(FILE *out, const struct line *lines, size_t count, siz
 	}
 }
 
-static int resize_lines(struct line **lines, size_t alloc)
+static int read_lines(FILE *in)
 {
-	struct line *result = realloc(*lines, alloc * sizeof **lines);
-	if (result) *lines = result;
-	else PERROR("Error allocating memory");
-	return !result;
-}
-
-static struct line *read_lines(FILE *in, size_t *count)
-{
-	size_t alloc = 16;
-	struct line *lines = NULL;
-
-	*count = 0;
-	if (resize_lines(&lines, alloc)) goto fail;
-
-	unsigned bits, addr = 0;
-	while (fscanf(in, " %x\n", &bits) > 0) {
-		if (addr > 0xffff) {
+	unsigned bits;
+	for (maxpc = 0; fscanf(in, " %x\n", &bits) > 0; maxpc += 2) {
+		if (maxpc > 0xffff) {
 			ERROR("Input exceeds 16-bit address space");
-			goto fail;
-		}
-		if (*count >= alloc && resize_lines(&lines, alloc *= 2)) {
-			goto fail;
+			return 1;
 		}
 
-		lines[*count] = (struct line) {
+		*LINE(maxpc) = (struct line) {
 			.mnem  = match_instruction(bits),
 			.value = bits,
-			.addr  = addr,
 		};
-
-		addr   += 2;
-		*count += 1;
 	}
 
-	return lines;
-
-fail:
-	free(lines);
-	return NULL;
+	return 0;
 }
 
 static void disassemble(FILE *in, FILE *out)
 {
-	size_t count;
-	struct line *lines = read_lines(in, &count);
-	if (!lines) return;
+	if (read_lines(in)) return;
+	assign_labels();
 
-	assign_labels(lines, count);
-
-	for (size_t i = 0; i < count; i++) {
-		const struct line *line  = lines + i;
+	for (size_t pc = 0; pc < maxpc; pc += 2) {
+		const struct line *line  = LINE(pc);
 		unsigned bits            = line->value;
 		const struct mnemonic *m = line->mnem;
 
@@ -175,12 +145,10 @@ static void disassemble(FILE *in, FILE *out)
 		for (int j = 0; j < 3 && m->operands[j].type; j++) {
 			if (j) fprintf(out, ", ");
 			else   fprintf(out, "%*s", 8 - (int)strlen(m->mnem), "");
-			print_operand(out, lines, count, i, j);
+			print_operand(out, pc, j);
 		}
 		fprintf(out, "\n");
 	}
-
-	free(lines);
 }
 
 static void usage(const char *progname)