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alu.c
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#include <stdint.h> // uint8_t.
#include <stdio.h> // FILE, f* functions.
#include "alu_op.h"
#define ROM_SIZE (1 << 17)
#define HALF_ZERO_FLAG_SET 0x1
#define HALF_CARRY_FLAG_SET 0x2
#define ZERO_FLAG_SET 0x4 // Only for low slice
#define IO_OE_FLAG_SET 0x8 // Only for low slice
#define CARRY_FLAG_SET 0x4 // Only for high slice
#define OVERFLOW_FLAG_SET 0x8 // Only for high slice
// Overflow flag reference:
// http://teaching.idallen.com/dat2343/10f/notes/040_overflow.txt
static uint8_t output_from_address(uint32_t i, uint8_t is_higher_half) {
uint8_t half_A = (i >> 0) & 0xf;
uint8_t half_B = (i >> 4) & 0xf;
uint8_t global_carry = (i >> 8) & 1;
ALU_OP operation = ((i >> 9) & 0x7) | (((i >> 13) & 0x3) << 3) | ((i >> 16) << 5); // 6 bits
uint8_t other_half_zero = (i >> 12) & 1;
uint8_t other_half_carry = (i >> 15) & 1;
if (operation >= 0x20) {
return (uint8_t)(half_A << 4);
}
ALU_OP op = operation; // & 0x1f;
switch (op) {
case ALU_OP_SET_IO_OE_FLAG: {
return is_higher_half ? 0 : IO_OE_FLAG_SET;
}
case ALU_OP_INC_LS: {
uint8_t q = is_higher_half ? half_A + other_half_carry : half_A + 1;
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (q & 0x10) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag =
global_carry ? CARRY_FLAG_SET : 0; // Preserve global carry.
uint8_t a_sign = (half_A >> 3);
uint8_t sum_sign = (half_q >> 3);
uint8_t alu_overflow_flag = (!a_sign && sum_sign)
? OVERFLOW_FLAG_SET
: 0x0;
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_DEC_LS: {
uint8_t q = is_higher_half ? (uint8_t)(half_A - other_half_carry)
: (uint8_t)(half_A - 1);
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (q & 0x10) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag =
global_carry ? CARRY_FLAG_SET : 0; // Preserve global carry.
uint8_t a_sign = (half_A >> 3);
uint8_t sum_sign = (half_q >> 3);
uint8_t alu_overflow_flag = (a_sign && !sum_sign)
? OVERFLOW_FLAG_SET
: 0x0;
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_LS_ADD_RS: {
uint8_t q = is_higher_half ? half_A + half_B + other_half_carry
: half_A + half_B;
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (q & 0x10) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag = half_carry ? CARRY_FLAG_SET : 0;
uint8_t a_sign = (half_A >> 3);
uint8_t b_sign = (half_B >> 3);
uint8_t sum_sign = (half_q >> 3);
uint8_t alu_overflow_flag =
((!a_sign && !b_sign && sum_sign) || (a_sign && b_sign && !sum_sign))
? OVERFLOW_FLAG_SET
: 0x0;
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_NOT_LS: {
uint8_t q = (uint8_t)~half_A;
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (q & 0x10) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag = 0; // Clear unconditionally
uint8_t alu_overflow_flag = 0; // Clear unconditionally
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_SHL_LS: {
uint8_t q = is_higher_half ? (uint8_t)(half_A << 1) | other_half_carry
: (uint8_t)(half_A << 1);
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (q & 0x10) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag =
is_higher_half && half_carry ? CARRY_FLAG_SET : 0;
uint8_t alu_overflow_flag = 0; // Clear unconditionally
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_SHR_LS: {
uint8_t q = is_higher_half
? (half_A >> 1)
: (uint8_t)(other_half_carry << 3) | (half_A >> 1);
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (half_A & 1) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag =
is_higher_half && other_half_carry ? CARRY_FLAG_SET : 0;
uint8_t alu_overflow_flag = 0; // Clear unconditionally
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_ROR_LS: {
uint8_t q = (uint8_t)(half_A >> 1) | (uint8_t)(other_half_carry << 3);
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (half_A & 1) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag =
is_higher_half && other_half_carry ? CARRY_FLAG_SET : 0;
uint8_t alu_overflow_flag = 0; // Clear unconditionally
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_LS_OR_RS: {
uint8_t half_q = half_A | half_B;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag = 0; // Clear unconditionally
uint8_t alu_overflow_flag = 0; // Clear unconditionally
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_LS_AND_RS: {
uint8_t half_q = half_A & half_B;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag = 0; // Clear unconditionally
uint8_t alu_overflow_flag = 0; // Clear unconditionally
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_LS_XOR_RS: {
uint8_t half_q = half_A ^ half_B;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag = 0; // Clear unconditionally
uint8_t alu_overflow_flag = 0; // Clear unconditionally
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_LS_ADC_RS: {
uint8_t q = is_higher_half ? half_A + half_B + other_half_carry
: half_A + half_B + global_carry;
uint8_t half_q = q & 0xf;
uint8_t half_zero = !half_q ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (q & 0x10) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
half_zero && other_half_zero ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag = half_carry ? CARRY_FLAG_SET : 0;
uint8_t a_sign = (half_A >> 3);
uint8_t b_sign = (half_B >> 3);
uint8_t sum_sign = (half_q >> 3);
uint8_t alu_overflow_flag =
((!a_sign && !b_sign && sum_sign) || (a_sign && b_sign && !sum_sign))
? OVERFLOW_FLAG_SET
: 0x0;
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
case ALU_OP_LS_SUB_RS: {
uint8_t q = is_higher_half ? (uint8_t)(half_A - (half_B + other_half_carry))
: (uint8_t)(half_A - half_B);
uint8_t half_q = q & 0xf;
uint8_t half_zero = half_q == 0 ? HALF_ZERO_FLAG_SET : 0;
uint8_t half_carry = (q & 0x10) ? HALF_CARRY_FLAG_SET : 0;
uint8_t alu_zero_flag =
(half_zero && other_half_zero) ? ZERO_FLAG_SET : 0;
uint8_t alu_carry_flag = half_carry ? CARRY_FLAG_SET : 0;
uint8_t a_sign = (half_A >> 3);
uint8_t b_sign = (half_B >> 3);
uint8_t sum_sign = (half_q >> 3);
uint8_t alu_overflow_flag =
((!a_sign && b_sign && sum_sign) || (a_sign && !b_sign && !sum_sign))
? OVERFLOW_FLAG_SET
: 0;
return half_zero | half_carry |
(is_higher_half ? alu_overflow_flag | alu_carry_flag
: alu_zero_flag) |
((uint8_t)(half_q << 4));
}
}
return 0;
}
static void generate_lookup_table(uint8_t (*low)[ROM_SIZE],
uint8_t (*high)[ROM_SIZE]) {
for (uint32_t i = 0; i < ROM_SIZE; ++i) {
(*low)[i] = output_from_address(i, 0);
(*high)[i] = output_from_address(i, 1);
}
}
static int write_to_file(const char *filename,
const uint8_t (*table)[ROM_SIZE]) {
FILE *file = fopen(filename, "wb");
if (file == NULL) {
perror(__func__);
return 1;
}
if (fwrite(*table, sizeof(*table), 1, file) == 0) {
perror(__func__);
return 2;
}
fclose(file);
return ferror(file);
}
int main(void) {
uint8_t low[ROM_SIZE] = {0};
uint8_t high[ROM_SIZE] = {0};
generate_lookup_table(&low, &high);
int error = write_to_file("bin/alu_low.bin", &low);
return error == 0 ? write_to_file("bin/alu_high.bin", &high) : error;
}