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Fix error in constant evaluation optimization #324

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Merged
jserv merged 2 commits into from
Jul 18, 2026
Merged

Fix error in constant evaluation optimization #324

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cc0516c
Fix signed constant modulo evaluation
tobiichi3227 Jul 18, 2026
0f68934
Reject zero divisors in constant expressions
tobiichi3227 Jul 18, 2026
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22 changes: 18 additions & 4 deletions src/parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
* shecc is freely redistributable under the BSD 2 clause license. See the
* file "LICENSE" for information on usage and redistribution of this file.
*/
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
Expand Down Expand Up @@ -3512,16 +3513,29 @@ int eval_expression_imm(opcode_t op, int op1, int op2)
res = op1 * op2;
break;
case OP_div:
if (!op2)
error_at("Division by zero in constant expression",
cur_token_loc());
res = op1 / op2;
break;
case OP_mod:
if (!op2)
error_at("Modulo by zero in constant expression", cur_token_loc());
/* Use bitwise AND for modulo optimization when divisor is power of 2 */
if (tmp == INT_MIN) {
res = op1 % op2;
break;
}
tmp = tmp < 0 ? -tmp : tmp;
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tmp &= (tmp - 1);
if ((op2 != 0) && (tmp == 0)) {
res = op1;
res &= (op2 - 1);
} else
if (tmp != 0) {
res = op1 % op2;
break;
}
op2 = op2 < 0 ? -op2 : op2;
res = op1 & (op2 - 1);
if (op1 < 0 && res != 0)
res -= op2;
break;
case OP_lshift:
res = op1 << op2;
Expand Down
21 changes: 21 additions & 0 deletions tests/driver.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -409,6 +409,27 @@ declare -a arithmetic_tests=(
run_expr_tests arithmetic_tests
expr 6 "111 % 7"

try_output 0 "1 1 -1 -1" << EOF
int v1 = 5 % 4;
int v2 = 5 % -4;
int v3 = -5 % 4;
int v4 = -5 % -4;
int main() {
printf("%d %d %d %d", v1, v2, v3, v4);
return 0;
}
EOF

try_compile_error << EOF
int value = 1 / 0;
int main() { return value; }
EOF

try_compile_error << EOF
int value = 1 % 0;
int main() { return value; }
EOF

# Category: Overflow Behavior
begin_category "Overflow Behavior" "Testing integer overflow handling"

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