Re: [Qemu-devel] [RFC v1 09/23] riscv: tcg-target: Add the immediate encoders

[Richard Henderson]

On 11/15/18 11:35 PM, Alistair Francis wrote:
> +static int32_t encode_simm12(uint32_t imm)
> +{
> +    return ((imm << 20) >> 25) << 25 | ((imm << 27) >> 27) << 7;
> +}

I'm not fond of triple shifts like this, as it makes me count.
I'd be ok with a formulation like

    return ((imm & 0x1f) << 7) | ((imm & 0xfe) << (25 - 5));

but perhaps best as

    uint32_t ret = 0;
    ret = deposit32(ret, imm, 7, 5);
    ret = deposit32(ret, imm >> 5, 25, 7);

Similarly with encode_sbimm12, encode_uimm20 (which is a simple &), 
encode_ujimm12.


r~