Re: [Qemu-devel] [PATCH v4 2/8] target/ppc: rework vmrg{l, h}{b, h, w} instructions to use Vsr* macros

[Mark Cave-Ayland]

On 29/01/2019 23:05, Richard Henderson wrote:

> On 1/29/19 11:17 AM, Mark Cave-Ayland wrote:
>> +#define VMRG_DO(name, element, access, ofs)                             \
>>      void helper_v##name(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b)       \
>>      {                                                                   \
>>          ppc_avr_t result;                                               \
>>          int i;                                                          \
>>                                                                          \
>> +        for (i = 0; i < ARRAY_SIZE(r->element) / 2; i++) {              \
>> +            result.access(i * 2 + 0) = a->access(i + ofs);              \
>> +            result.access(i * 2 + 1) = b->access(i + ofs);              \
>>          }                                                               \
>>          *r = result;                                                    \
>>      }
>> +
>> +#define VMRG(suffix, element, access, half)        \
>> +    VMRG_DO(mrgl##suffix, element, access, half)   \
>> +    VMRG_DO(mrgh##suffix, element, access, 0)
>> +VMRG(b, u8, VsrB, 8)
>> +VMRG(h, u16, VsrH, 4)
>> +VMRG(w, u32, VsrW, 2)
> 
> So... the point of "half" was to not replicate knowledge out to VMRG.
> Just use
> 
>     int i, half = ARRAY_SIZE(r->element) / 2;
>     for (i = 0; i < half; i++) {
> 
> within VMRG_DO.

Okay - I was a bit confused because in your example macro signature you added 
ofs
which made me think you wanted its value to be determined outside, but never 
mind.

What about the following instead? With high set as part of the macro then the 
initial
assignment to ofs should be inlined accordingly at compile time:


#define VMRG_DO(name, element, access, high)                                 \
    void helper_v##name(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b)            \
    {                                                                        \
        ppc_avr_t result;                                                    \
        int ofs, half = ARRAY_SIZE(r->element) / 2;                          \
        int i;                                                               \
                                                                             \
        if (high) {                                                          \
            ofs = 0;                                                         \
        } else {                                                             \
            ofs = half;                                                      \
        }                                                                    \
                                                                             \
        for (i = 0; i < half; i++) {                                         \
            result.access(i * 2 + 0) = a->access(i + ofs);                   \
            result.access(i * 2 + 1) = b->access(i + ofs);                   \
        }                                                                    \
        *r = result;                                                         \
    }

#define VMRG(suffix, element, access)          \
    VMRG_DO(mrgl##suffix, element, access, 0)  \
    VMRG_DO(mrgh##suffix, element, access, 1)
VMRG(b, u8, VsrB)
VMRG(h, u16, VsrH)
VMRG(w, u32, VsrW)
#undef VMRG_DO
#undef VMRG
#undef VMRG


ATB,

Mark.