Merge #1250: No need to subtract 1 before doing a right shift

jonasnick · jonasnick · commit 1d8f367515f0 · 2023-03-28T06:32:28.000Z
3e43041 No need to subtract 1 before doing a right shift (roconnor-blockstream) Pull request description: ACKs for top commit: real-or-random: utACK 3e43041 jonasnick: ACK 3e43041 Tree-SHA512: bcecda11eae3fb845bef7af88c6171bedcd933872d08a9849c0a250cb6c9e982a88bd45e8a8364a4a348f8be413fc91ee04cf8fa78adae44e584e3ad7ec544cf
diff --git a/src/int128_struct_impl.h b/src/int128_struct_impl.h
@@ -193,7 +193,7 @@ static SECP256K1_INLINE int secp256k1_i128_check_pow2(const secp256k1_int128 *r,
     VERIFY_CHECK(n < 127);
     VERIFY_CHECK(sign == 1 || sign == -1);
     return n >= 64 ? r->hi == (uint64_t)sign << (n - 64) && r->lo == 0
-                   : r->hi == (uint64_t)((sign - 1) >> 1) && r->lo == (uint64_t)sign << n;
+                   : r->hi == (uint64_t)(sign >> 1) && r->lo == (uint64_t)sign << n;
 }
 
 #endif

Original file line number	Diff line number	Diff line change
`@@ -193,7 +193,7 @@ static SECP256K1_INLINE int secp256k1_i128_check_pow2(const secp256k1_int128 *r,`
`193`	`193`	`VERIFY_CHECK(n < 127);`
`194`	`194`	`VERIFY_CHECK(sign == 1 \|\| sign == -1);`
`195`	`195`	`return n >= 64 ? r->hi == (uint64_t)sign << (n - 64) && r->lo == 0`
`196`		`- : r->hi == (uint64_t)((sign - 1) >> 1) && r->lo == (uint64_t)sign << n;`
	`196`	`+ : r->hi == (uint64_t)(sign >> 1) && r->lo == (uint64_t)sign << n;`
`197`	`197`	`}`
`198`	`198`
`199`	`199`	`#endif`