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Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtr
Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions
Sat, 14 Mar 2020 14:08:41 +0800
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On 2020/3/14 13:58, Richard Henderson wrote:
On 3/12/20 7:58 AM, LIU Zhiwei wrote:
+#define DO_MADC(N, M, C) ((__typeof(N))(N + M + C) < N ? 1 : 0)
Incorrect. E.g N = 1, M = UINT_MAX, C = 1, adds to 1, which is not less than
N, despite the carry-out.
Yes, it really the corner case. I should test C first.
Thanks for pointing that.
C ? N + M <= N : N + M < N
+#define DO_MSBC(N, M, C) ((__typeof(N))(N - M - C) > N ? 1 : 0)
C ? N <= M : N < M