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

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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~

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Re: [PATCH v5 08/60] target/riscv: add vector amo operations, (continued)
- [PATCH v5 09/60] target/riscv: vector single-width integer add and subtract, LIU Zhiwei, 2020/03/12
  - Re: [PATCH v5 09/60] target/riscv: vector single-width integer add and subtract, Richard Henderson, 2020/03/14
    - Re: [PATCH v5 09/60] target/riscv: vector single-width integer add and subtract, LIU Zhiwei, 2020/03/14
    - Re: [PATCH v5 09/60] target/riscv: vector single-width integer add and subtract, LIU Zhiwei, 2020/03/23
    - Re: [PATCH v5 09/60] target/riscv: vector single-width integer add and subtract, Richard Henderson, 2020/03/23
- [PATCH v5 10/60] target/riscv: vector widening integer add and subtract, LIU Zhiwei, 2020/03/12
  - Re: [PATCH v5 10/60] target/riscv: vector widening integer add and subtract, Richard Henderson, 2020/03/14
- [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions, LIU Zhiwei, 2020/03/12
  - Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions, Richard Henderson, 2020/03/14
    - Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions, LIU Zhiwei <=
    - Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions, Richard Henderson, 2020/03/14
    - Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions, LIU Zhiwei, 2020/03/14
- [PATCH v5 12/60] target/riscv: vector bitwise logical instructions, LIU Zhiwei, 2020/03/12
  - Re: [PATCH v5 12/60] target/riscv: vector bitwise logical instructions, Richard Henderson, 2020/03/14
- [PATCH v5 13/60] target/riscv: vector single-width bit shift instructions, LIU Zhiwei, 2020/03/12
  - Re: [PATCH v5 13/60] target/riscv: vector single-width bit shift instructions, Richard Henderson, 2020/03/14
- [PATCH v5 14/60] target/riscv: vector narrowing integer right shift instructions, LIU Zhiwei, 2020/03/12
  - Re: [PATCH v5 14/60] target/riscv: vector narrowing integer right shift instructions, Richard Henderson, 2020/03/14
- [PATCH v5 15/60] target/riscv: vector integer comparison instructions, LIU Zhiwei, 2020/03/12
  - Re: [PATCH v5 15/60] target/riscv: vector integer comparison instructions, Richard Henderson, 2020/03/14

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