StackRduino
diff --git a/‎py/mpz.c‎
Lines changed: 9 additions & 6 deletions b/‎py/mpz.c‎
Lines changed: 9 additions & 6 deletions
@@ -308,9 +308,13 @@ STATIC mp_uint_t mpn_or_neg(mpz_dig_t *idig, const mpz_dig_t *jdig, mp_uint_t jl
         carryi >>= DIG_SIZE;
     }
 
-    if (0 != carryi) {
-        *idig++ = carryi;
-    }
+    // At least one of j,k must be negative so the above for-loop runs at least
+    // once.  For carryi to be non-zero here it must be equal to 1 at the end of
+    // each iteration of the loop.  So the accumulation of carryi must overflow
+    // each time, ie carryi += 0xff..ff.  So carryj|carryk must be 0 in the
+    // DIG_MASK bits on each iteration.  But considering all cases of signs of
+    // j,k one sees that this is not possible.
+    assert(carryi == 0);
 
     return mpn_remove_trailing_zeros(oidig, idig);
 }
@@ -334,9 +338,8 @@ STATIC mp_uint_t mpn_or_neg(mpz_dig_t *idig, const mpz_dig_t *jdig, mp_uint_t jl
         carryi >>= DIG_SIZE;
     }
 
-    if (0 != carryi) {
-        *idig++ = carryi;
-    }
+    // See comment in above mpn_or_neg for why carryi must be 0.
+    assert(carryi == 0);
 
     return mpn_remove_trailing_zeros(oidig, idig);
 }
Original file line number	Diff line number	Diff line change
`@@ -308,9 +308,13 @@ STATIC mp_uint_t mpn_or_neg(mpz_dig_t idig, const mpz_dig_t jdig, mp_uint_t jl`
`308`	`308`	`carryi >>= DIG_SIZE;`
`309`	`309`	`}`
`310`	`310`
`311`		`- if (0 != carryi) {`
`312`		`- *idig++ = carryi;`
`313`		`- }`
	`311`	`+ // At least one of j,k must be negative so the above for-loop runs at least`
	`312`	`+ // once. For carryi to be non-zero here it must be equal to 1 at the end of`
	`313`	`+ // each iteration of the loop. So the accumulation of carryi must overflow`
	`314`	`+ // each time, ie carryi += 0xff..ff. So carryj\|carryk must be 0 in the`
	`315`	`+ // DIG_MASK bits on each iteration. But considering all cases of signs of`
	`316`	`+ // j,k one sees that this is not possible.`
	`317`	`+ assert(carryi == 0);`
`314`	`318`
`315`	`319`	`return mpn_remove_trailing_zeros(oidig, idig);`
`316`	`320`	`}`
`@@ -334,9 +338,8 @@ STATIC mp_uint_t mpn_or_neg(mpz_dig_t idig, const mpz_dig_t jdig, mp_uint_t jl`
`334`	`338`	`carryi >>= DIG_SIZE;`
`335`	`339`	`}`
`336`	`340`
`337`		`- if (0 != carryi) {`
`338`		`- *idig++ = carryi;`
`339`		`- }`
	`341`	`+ // See comment in above mpn_or_neg for why carryi must be 0.`
	`342`	`+ assert(carryi == 0);`
`340`	`343`
`341`	`344`	`return mpn_remove_trailing_zeros(oidig, idig);`
`342`	`345`	`}`