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Support modulo operator #27

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merged 1 commit into from
Nov 5, 2020
Merged

Support modulo operator #27

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19 changes: 19 additions & 0 deletions src/cfront.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,7 @@ typedef enum {
T_close_square, /* ] */
T_asterisk, /* '*' */
T_divide, /* / */
T_mod, /* % */
T_bit_or, /* | */
T_bit_xor, /* ^ */
T_log_and, /* && */
Expand Down Expand Up @@ -338,6 +339,10 @@ token_t get_next_token()
skip_whitespace();
return T_lt;
}
if (next_char == '%') {
read_char(1);
return T_mod;
}
if (next_char == '>') {
read_char(0);
if (next_char == '=') {
Expand Down Expand Up @@ -876,6 +881,7 @@ int get_operator_prio(opcode_t op)
return 12;
case OP_mul:
case OP_div:
case OP_mod:
return 13;
default:
return 0;
Expand All @@ -893,6 +899,8 @@ opcode_t get_operator()
op = OP_mul;
else if (lex_accept(T_divide))
op = OP_div;
else if (lex_accept(T_mod))
op = OP_mod;
else if (lex_accept(T_lshift))
op = OP_lshift;
else if (lex_accept(T_rshift))
Expand Down Expand Up @@ -1357,6 +1365,7 @@ int read_numeric_sconstant()
int eval_expression_imm(opcode_t op, int op1, int op2)
{
/* return immediate result */
int tmp = op2;
int res = 0;
switch (op) {
case OP_add:
Expand All @@ -1371,6 +1380,16 @@ int eval_expression_imm(opcode_t op, int op1, int op2)
case OP_div:
res = op1 / op2;
break;
case OP_mod:
/* TODO: provide arithmetic & operation instead of '&=' */
/* TODO: do optimization for local expression */
tmp &= (tmp - 1);
if ((op2 != 0) && (tmp == 0)) {
res = op1;
res &= (op2 - 1);
} else
res = op1 % op2;
break;
case OP_lshift:
res = op1 << op2;
break;
Expand Down
9 changes: 9 additions & 0 deletions src/codegen.c
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Expand Up @@ -121,6 +121,7 @@ int get_code_length(ir_instr_t *ii)
case OP_func_exit:
return 16;
case OP_exit:
case OP_mod:
return 12;
case OP_load_data_address:
case OP_jz:
Expand Down Expand Up @@ -367,6 +368,14 @@ void code_generate()
if (dump_ir == 1)
printf(" x%d /= x%d", dest_reg, OP_reg);
break;
case OP_mod:
emit(__div(__AL, OP_reg + 1, OP_reg, dest_reg));
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Both div and mul instruction are heavier. Instead, you can add shortcut for power-of-2. That is, convert the original modulo operation into n & (d - 1) if d is power-of-2. You should implement the shortcut in src/cfront.c.

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I think only global expression can do this shortcut because shecc can't determine the value of operand in local expression before execution time. Can we ignore optimization for local expression in this patch?

BTW, relative issue#28 and detailed information was sent.

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Sure, let's merge this change first. Do append the comments with TODO: optimize ...

emit(__mul(__AL, OP_reg, OP_reg, OP_reg + 1));
emit(__sub_r(__AL, dest_reg, dest_reg, OP_reg));
/* TODO: support percent-sign character (%) in format string */
if (dump_ir == 1)
printf(" x%d = x%d mod x%d", dest_reg, dest_reg, OP_reg);
break;
case OP_negate:
emit(__rsb_i(__AL, dest_reg, 0, dest_reg));
if (dump_ir == 1)
Expand Down
1 change: 1 addition & 0 deletions src/defs.h
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Expand Up @@ -68,6 +68,7 @@ typedef enum {
OP_sub,
OP_mul,
OP_div, /* signed division */
OP_mod, /* modulo */
OP_lshift,
OP_rshift,
OP_log_and,
Expand Down
4 changes: 2 additions & 2 deletions tests/driver.sh
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Expand Up @@ -69,8 +69,8 @@ expr 55 "1 + (2 + (3 + (4 + (5 + (6 + (7 + (8 + (9 + 10))))))))"
# expr 21 "+1+20"
# expr 10 "-15+(+35-10)"

# expr 2 "5 % 3"
# expr 6 "111 % 7"
expr 2 "5 % 3"
expr 6 "111 % 7"

expr 1 "10 > 5"
expr 1 "3+3 > 5"
Expand Down