py/runtime: Optimise mp_small_int_mul_overflow result.

dpgeorge · projectgus · commit 58be838bf5a2 · 2025-07-15T11:26:02.000+10:00
Signed-off-by: Damien George &lt;damien@micropython.org&gt;
diff --git a/py/runtime.c b/py/runtime.c
@@ -422,7 +422,6 @@ mp_obj_t MICROPY_WRAP_MP_BINARY_OP(mp_binary_op)(mp_binary_op_t op, mp_obj_t lhs
     }
 
     if (mp_obj_is_small_int(lhs)) {
-        mp_int_t int_res;
         mp_int_t lhs_val = MP_OBJ_SMALL_INT_VALUE(lhs);
         if (mp_obj_is_small_int(rhs)) {
             mp_int_t rhs_val = MP_OBJ_SMALL_INT_VALUE(rhs);
@@ -506,6 +505,7 @@ mp_obj_t MICROPY_WRAP_MP_BINARY_OP(mp_binary_op)(mp_binary_op_t op, mp_obj_t lhs
                     }
                     #endif
 
+                    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);
@@ -553,15 +553,15 @@ 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, &int_res)) {
+                                if (mp_small_int_mul_overflow(ans, lhs_val, &ans)) {
                                     goto power_overflow;
                                 }
-                                ans = int_res;
                             }
                             if (rhs_val == 1) {
                                 break;
                             }
                             rhs_val /= 2;
+                            mp_int_t int_res;
                             if (mp_small_int_mul_overflow(lhs_val, lhs_val, &int_res)) {
                                 goto power_overflow;
                             }

Original file line number	Diff line number	Diff line change
`@@ -422,7 +422,6 @@ mp_obj_t MICROPY_WRAP_MP_BINARY_OP(mp_binary_op)(mp_binary_op_t op, mp_obj_t lhs`
`422`	`422`	`}`
`423`	`423`
`424`	`424`	`if (mp_obj_is_small_int(lhs)) {`
`425`		`- mp_int_t int_res;`
`426`	`425`	`mp_int_t lhs_val = MP_OBJ_SMALL_INT_VALUE(lhs);`
`427`	`426`	`if (mp_obj_is_small_int(rhs)) {`
`428`	`427`	`mp_int_t rhs_val = MP_OBJ_SMALL_INT_VALUE(rhs);`
`@@ -506,6 +505,7 @@ mp_obj_t MICROPY_WRAP_MP_BINARY_OP(mp_binary_op)(mp_binary_op_t op, mp_obj_t lhs`
`506`	`505`	`}`
`507`	`506`	`#endif`
`508`	`507`
	`508`	`+ mp_int_t int_res;`
`509`	`509`	`if (mp_small_int_mul_overflow(lhs_val, rhs_val, &int_res)) {`
`510`	`510`	`// use higher precision`
`511`	`511`	`lhs = mp_obj_new_int_from_ll(lhs_val);`
`@@ -553,15 +553,15 @@ mp_obj_t MICROPY_WRAP_MP_BINARY_OP(mp_binary_op)(mp_binary_op_t op, mp_obj_t lhs`
`553`	`553`	`mp_int_t ans = 1;`
`554`	`554`	`while (rhs_val > 0) {`
`555`	`555`	`if (rhs_val & 1) {`
`556`		`- if (mp_small_int_mul_overflow(ans, lhs_val, &int_res)) {`
	`556`	`+ if (mp_small_int_mul_overflow(ans, lhs_val, &ans)) {`
`557`	`557`	`goto power_overflow;`
`558`	`558`	`}`
`559`		`- ans = int_res;`
`560`	`559`	`}`
`561`	`560`	`if (rhs_val == 1) {`
`562`	`561`	`break;`
`563`	`562`	`}`
`564`	`563`	`rhs_val /= 2;`
	`564`	`+ mp_int_t int_res;`
`565`	`565`	`if (mp_small_int_mul_overflow(lhs_val, lhs_val, &int_res)) {`
`566`	`566`	`goto power_overflow;`
`567`	`567`	`}`