qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtr


From: LIU Zhiwei
Subject: Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions
Date: Sat, 14 Mar 2020 14:08:41 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0



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.

Zhiwei

You want

     C ? N + M <= N : N + M < N

+#define DO_MSBC(N, M, C) ((__typeof(N))(N - M - C) > N ? 1 : 0)
Similarly

     C ? N <= M : N < M


r~




reply via email to

[Prev in Thread] Current Thread [Next in Thread]