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Can read from variables in expressions.

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This commit is contained in:
Lawrence Kesteloot 2018-08-03 13:19:29 -07:00
parent fd8aa963d4
commit 0d579ce354
1 changed files with 82 additions and 58 deletions
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140
main.c
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@ -16,8 +16,10 @@ uint8_t title_length = 9;
#define I_STX_ZPG 0x86
#define I_STA_IND_Y 0x91
#define I_LDY_IMM 0xA0
#define I_LDX 0xA2
#define I_LDA 0xA9
#define I_LDX_IMM 0xA2
#define I_LDA_ZPG 0xA5
#define I_LDX_ZPG 0xA6
#define I_LDA_IMM 0xA9
// Tokens.
#define T_HOME 0x80
@ -221,12 +223,63 @@ static uint16_t parse_uint16(uint8_t **s_ptr) {
* Generate code to put the value into AX.
*/
static void compile_load_ax(uint16_t value) {
g_compiled[g_compiled_length++] = I_LDX;
g_compiled[g_compiled_length++] = I_LDX_IMM;
g_compiled[g_compiled_length++] = value >> 8;
g_compiled[g_compiled_length++] = I_LDA;
g_compiled[g_compiled_length++] = I_LDA_IMM;
g_compiled[g_compiled_length++] = value & 0xFF;
}
/**
* Find a variable by name. Only the first two letters are considered.
* Advances the pointer past the variable name (including letters after
* the first two). Returns the memory address of the variable. If we
* ran out of space for variables, returns OUT_OF_VARIABLE_SPACE
* and does not modify the buffer pointer.
*/
static uint8_t find_variable(uint8_t **buffer) {
uint8_t *s = *buffer;
uint8_t *existing_name = g_variable_names;
uint8_t name[2];
int16_t var;
// Pull out the variable name.
name[0] = *s++;
if (*s != 0 && (*s & 0x80) == 0) {
name[1] = *s++;
} else {
name[1] = 0;
}
// Skip rest of name.
while (*s != 0 && (*s & 0x80) == 0) {
s++;
}
for (var = 0; var < MAX_VARIABLES; var++) {
if (existing_name[0] == 0 && existing_name[1] == 0) {
// First free entry. Allocate it.
existing_name[0] = name[0];
existing_name[1] = name[1];
break;
} else if (existing_name[0] == name[0] && existing_name[1] == name[1]) {
// Found it.
break;
}
existing_name += 2;
}
if (var == MAX_VARIABLES) {
var = OUT_OF_VARIABLE_SPACE;
} else {
// Convert index to address.
var = FIRST_VARIABLE + 2*var;
// Advance pointer.
*buffer = s;
}
return (uint8_t) var;
}
/**
* Parse an expression, generating code to compute it, leaving the
* result in AX.
@ -248,6 +301,28 @@ static uint8_t *compile_expression(uint8_t *s) {
value = parse_uint16(&s);
compile_load_ax(value);
have_value_in_ax = 1;
} else if (*s >= 'A' && *s <= 'Z') {
// Variable reference.
uint8_t var = find_variable(&s);
if (have_value_in_ax) {
// Push on the number stack.
add_call(pushax);
}
if (var == OUT_OF_VARIABLE_SPACE) {
// TODO: Not sure how to deal with this. For now just
// fill in with zero, since assigning to this elsewhere
// will cause an error.
compile_load_ax(0);
} else {
// Load from var.
g_compiled[g_compiled_length++] = I_LDA_ZPG;
g_compiled[g_compiled_length++] = var;
g_compiled[g_compiled_length++] = I_LDX_ZPG;
g_compiled[g_compiled_length++] = var + 1;
}
have_value_in_ax = 1;
} else if (*s == T_PLUS) {
plus_count += 1;
s += 1;
@ -331,57 +406,6 @@ static uint8_t *find_line(uint16_t line_number) {
return line;
}
/**
* Find a variable by name. Only the first two letters are considered.
* Advances the pointer past the variable name (including letters after
* the first two). Returns the memory address of the variable. If we
* ran out of space for variables, returns OUT_OF_VARIABLE_SPACE
* and does not modify the buffer pointer.
*/
static uint8_t find_variable(uint8_t **buffer) {
uint8_t *s = *buffer;
uint8_t *existing_name = g_variable_names;
uint8_t name[2];
int16_t var;
// Pull out the variable name.
name[0] = *s++;
if (*s != 0 && (*s & 0x80) == 0) {
name[1] = *s++;
} else {
name[1] = 0;
}
// Skip rest of name.
while (*s != 0 && (*s & 0x80) == 0) {
s++;
}
for (var = 0; var < MAX_VARIABLES; var++) {
if (existing_name[0] == 0 && existing_name[1] == 0) {
// First free entry. Allocate it.
existing_name[0] = name[0];
existing_name[1] = name[1];
break;
} else if (existing_name[0] == name[0] && existing_name[1] == name[1]) {
// Found it.
break;
}
existing_name += 2;
}
if (var == MAX_VARIABLES) {
var = OUT_OF_VARIABLE_SPACE;
} else {
// Convert index to address.
var = FIRST_VARIABLE + 2*var;
// Advance pointer.
*buffer = s;
}
return (uint8_t) var;
}
/**
* Call to configure the compilation step.
*/
@ -404,8 +428,8 @@ static void compile_buffer(uint8_t *buffer, uint16_t line_number) {
if (*s == '\0' || *s == ':') {
// Empty statement. We skip the colon below.
} else if ((*s & 0x80) == 0) {
// Not a token. Must be variable assignment.
} else if (*s >= 'A' && *s <= 'Z') {
// Must be variable assignment.
uint8_t var = find_variable(&s);
if (var == OUT_OF_VARIABLE_SPACE) {
// TODO: Nicer error specifically for out of variable space.
@ -430,7 +454,7 @@ static void compile_buffer(uint8_t *buffer, uint16_t line_number) {
} else if (*s == T_PRINT) {
s += 1;
if (*s >= '0' && *s <= '9') { // TODO: Add negative sign and open parenthesis.
if (*s != '\0' && *s != ':') {
// Parse expression.
s = compile_expression(s);
add_call(print_int);