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py/smallint: Update mp_small_int_mul_overflow() to perform the multiply.

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Makes it compatible with the __builtin_mul_overflow() syntax, used in
follow-up commit.

Includes optimisation in runtime.c to minimise the code size impact from
additional param.

Signed-off-by: Damien George <damien@micropython.org>
Signed-off-by: Angus Gratton <angus@redyak.com.au>
This commit is contained in:
Angus Gratton
2025-05-02 15:39:35 +10:00
committed by Damien George
parent 516aa02104
commit e9845ab20e
4 changed files with 17 additions and 10 deletions
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4
py/parsenum.c
View File

@@ -99,10 +99,10 @@ mp_obj_t mp_parse_num_integer(const char *restrict str_, size_t len, int base, m
}
// add next digi and check for overflow
if (mp_small_int_mul_overflow(int_val, base)) {
if (mp_small_int_mul_overflow(int_val, base, &int_val)) {
goto overflow;
}
int_val = int_val * base + dig;
int_val += dig;
if (!MP_SMALL_INT_FITS(int_val)) {
goto overflow;
}

13
py/runtime.c
View File

@@ -505,13 +505,14 @@ mp_obj_t MICROPY_WRAP_MP_BINARY_OP(mp_binary_op)(mp_binary_op_t op, mp_obj_t lhs
}
#endif
if (mp_small_int_mul_overflow(lhs_val, rhs_val)) {
mp_int_t int_res;
if (mp_small_int_mul_overflow(lhs_val, rhs_val, &int_res)) {
// use higher precision
lhs = mp_obj_new_int_from_ll(lhs_val);
goto generic_binary_op;
} else {
// use standard precision
return MP_OBJ_NEW_SMALL_INT(lhs_val * rhs_val);
return MP_OBJ_NEW_SMALL_INT(int_res);
}
}
case MP_BINARY_OP_FLOOR_DIVIDE:
@@ -552,19 +553,19 @@ mp_obj_t MICROPY_WRAP_MP_BINARY_OP(mp_binary_op)(mp_binary_op_t op, mp_obj_t lhs
mp_int_t ans = 1;
while (rhs_val > 0) {
if (rhs_val & 1) {
if (mp_small_int_mul_overflow(ans, lhs_val)) {
if (mp_small_int_mul_overflow(ans, lhs_val, &ans)) {
goto power_overflow;
}
ans *= lhs_val;
}
if (rhs_val == 1) {
break;
}
rhs_val /= 2;
if (mp_small_int_mul_overflow(lhs_val, lhs_val)) {
mp_int_t int_res;
if (mp_small_int_mul_overflow(lhs_val, lhs_val, &int_res)) {
goto power_overflow;
}
lhs_val *= lhs_val;
lhs_val = int_res;
}
lhs_val = ans;
}

5
py/smallint.c
View File

@@ -26,7 +26,7 @@
#include "py/smallint.h"
bool mp_small_int_mul_overflow(mp_int_t x, mp_int_t y) {
bool mp_small_int_mul_overflow(mp_int_t x, mp_int_t y, mp_int_t *res) {
// Check for multiply overflow; see CERT INT32-C
if (x > 0) { // x is positive
if (y > 0) { // x and y are positive
@@ -49,6 +49,9 @@ bool mp_small_int_mul_overflow(mp_int_t x, mp_int_t y) {
}
} // End if x and y are nonpositive
} // End if x is nonpositive
// Result doesn't overflow
*res = x * y;
return false;
}

5
py/smallint.h
View File

@@ -68,7 +68,10 @@
// The number of bits in a MP_SMALL_INT including the sign bit.
#define MP_SMALL_INT_BITS (MP_IMAX_BITS(MP_SMALL_INT_MAX) + 1)
bool mp_small_int_mul_overflow(mp_int_t x, mp_int_t y);
// Multiply two small ints.
// If returns false, the correct result is stored in 'res'
// If returns true, the multiplication would have overflowed. 'res' is unchanged.
bool mp_small_int_mul_overflow(mp_int_t x, mp_int_t y, mp_int_t *res);
mp_int_t mp_small_int_modulo(mp_int_t dividend, mp_int_t divisor);
mp_int_t mp_small_int_floor_divide(mp_int_t num, mp_int_t denom);