For this reason, GLSL 4.0 introduces the 'precise' qualifier. I invite
you to take a look at this article.
2014/1/6 Roland Scheidegger <srol...@vmware.com>:
> Am 05.01.2014 01:34, schrieb Maxence Le Doré:
>> FMA(a,b,c) keeps extra precision (usually 1 more bit of mantissa,
>> afaik) for the result a*b and add this to c, to finally produce a
>> IEEE754 32bit float result.
>>
>> MAD(a,b,c) product a IEEE754 32bit float product a*b and add it to C.
>>
>> So, fma can be slightly more accurate. An accuracy that is something
>> very appreciate.
>
> Actually in "newer" languages (such as opencl) "mad" is used to indicate
> intermediate rounding does not matter, so if your cpu can do fma but not
> mul+add in a single cycle it is allowed to use fma instead.
> FMA OTOH of course forces no intermediate rounding.
> Our tgsi definitions certainly initially were meaning intermediate
> rounding should take place, I don't know if we need to keep it that way
> or could repurpose that slightly (so if you require the intermediate
> rounding you'd just use mul+add).
>
> Roland
>
>
>
>>
>>
>> 2014/1/5 Marek Olšák <mar...@gmail.com>:
>>> How is FMA different from MAD?
>>>
>>> Please document the new opcodes in src/gallium/docs/source/tgsi.rst.
>>>
>>> Marek
>>>
>>> On Sun, Jan 5, 2014 at 12:42 AM, Maxence Le Doré
>>> <maxence.led...@gmail.com> wrote:
>>>> From: Maxence Le Doré <Maxence Le Doré>
>>>>
>>>> ---
>>>> src/gallium/auxiliary/tgsi/tgsi_info.c | 16 ++++++++++++++++
>>>> src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h | 6 ++++++
>>>> src/gallium/include/pipe/p_shader_tokens.h | 9 ++++++++-
>>>> 3 files changed, 30 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_info.c
>>>> b/src/gallium/auxiliary/tgsi/tgsi_info.c
>>>> index 0beef44..ed55940 100644
>>>> --- a/src/gallium/auxiliary/tgsi/tgsi_info.c
>>>> +++ b/src/gallium/auxiliary/tgsi/tgsi_info.c
>>>> @@ -221,6 +221,12 @@ static const struct tgsi_opcode_info
>>>> opcode_info[TGSI_OPCODE_LAST] =
>>>> { 1, 3, 1, 0, 0, 0, OTHR, "TXL2", TGSI_OPCODE_TXL2 },
>>>> { 1, 2, 0, 0, 0, 0, COMP, "IMUL_HI", TGSI_OPCODE_IMUL_HI },
>>>> { 1, 2, 0, 0, 0, 0, COMP, "UMUL_HI", TGSI_OPCODE_UMUL_HI },
>>>> + { 1, 3, 0, 0, 0, 0, COMP, "FMA", TGSI_OPCODE_FMA },
>>>> + { 1, 1, 0, 0, 0, 0, COMP, "POPCNT", TGSI_OPCODE_POPCNT },
>>>> + { 1, 1, 0, 0, 0, 0, COMP, "IMSB", TGSI_OPCODE_IMSB },
>>>> + { 1, 1, 0, 0, 0, 0, COMP, "ILSB", TGSI_OPCODE_ILSB },
>>>> + { 1, 1, 0, 0, 0, 0, COMP, "UMSB", TGSI_OPCODE_UMSB },
>>>> + { 1, 1, 0, 0, 0, 0, COMP, "ULSB", TGSI_OPCODE_ULSB },
>>>> };
>>>>
>>>> const struct tgsi_opcode_info *
>>>> @@ -321,6 +327,11 @@ tgsi_opcode_infer_type( uint opcode )
>>>> case TGSI_OPCODE_IABS:
>>>> case TGSI_OPCODE_ISSG:
>>>> case TGSI_OPCODE_IMUL_HI:
>>>> + case TGSI_OPCODE_POPCNT:
>>>> + case TGSI_OPCODE_ILSB:
>>>> + case TGSI_OPCODE_IMSB:
>>>> + case TGSI_OPCODE_ULSB:
>>>> + case TGSI_OPCODE_UMSB:
>>>> return TGSI_TYPE_SIGNED;
>>>> default:
>>>> return TGSI_TYPE_FLOAT;
>>>> @@ -344,9 +355,14 @@ tgsi_opcode_infer_src_type( uint opcode )
>>>> case TGSI_OPCODE_SAMPLE_I:
>>>> case TGSI_OPCODE_SAMPLE_I_MS:
>>>> case TGSI_OPCODE_UMUL_HI:
>>>> + case TGSI_OPCODE_POPCNT:
>>>> + case TGSI_OPCODE_ULSB:
>>>> + case TGSI_OPCODE_UMSB:
>>>> return TGSI_TYPE_UNSIGNED;
>>>> case TGSI_OPCODE_IMUL_HI:
>>>> case TGSI_OPCODE_I2F:
>>>> + case TGSI_OPCODE_ILSB:
>>>> + case TGSI_OPCODE_IMSB:
>>>> return TGSI_TYPE_SIGNED;
>>>> case TGSI_OPCODE_ARL:
>>>> case TGSI_OPCODE_ARR:
>>>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h
>>>> b/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h
>>>> index 1ef78dd..cba0975 100644
>>>> --- a/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h
>>>> +++ b/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h
>>>> @@ -206,6 +206,12 @@ OP13(UCMP)
>>>>
>>>> OP12(IMUL_HI)
>>>> OP12(UMUL_HI)
>>>> +OP13(FMA)
>>>> +OP11(POPCNT)
>>>> +OP11(IMSB)
>>>> +OP11(ILSB)
>>>> +OP11(UMSB)
>>>> +OP11(ULSB)
>>>>
>>>> #undef OP00
>>>> #undef OP01
>>>> diff --git a/src/gallium/include/pipe/p_shader_tokens.h
>>>> b/src/gallium/include/pipe/p_shader_tokens.h
>>>> index 8010902..5ed0c34 100644
>>>> --- a/src/gallium/include/pipe/p_shader_tokens.h
>>>> +++ b/src/gallium/include/pipe/p_shader_tokens.h
>>>> @@ -453,7 +453,14 @@ struct tgsi_property_data {
>>>> #define TGSI_OPCODE_IMUL_HI 180
>>>> #define TGSI_OPCODE_UMUL_HI 181
>>>>
>>>> -#define TGSI_OPCODE_LAST 182
>>>> +#define TGSI_OPCODE_FMA 182
>>>> +#define TGSI_OPCODE_POPCNT 183
>>>> +#define TGSI_OPCODE_IMSB 184
>>>> +#define TGSI_OPCODE_ILSB 185
>>>> +#define TGSI_OPCODE_UMSB 186
>>>> +#define TGSI_OPCODE_ULSB 187
>>>> +
>>>> +#define TGSI_OPCODE_LAST 188
>>>>
>>>> #define TGSI_SAT_NONE 0 /* do not saturate */
>>>> #define TGSI_SAT_ZERO_ONE 1 /* clamp to [0,1] */
>>>> --
>>>> 1.8.5.2
>>>>
>>>> _______________________________________________
>>>> mesa-dev mailing list
>>>> mesa-dev@lists.freedesktop.org
>>>> https://urldefense.proofpoint.com/v1/url?u=http://lists.freedesktop.org/mailman/listinfo/mesa-dev&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=F4msKE2WxRzA%2BwN%2B25muztFm5TSPwE8HKJfWfR2NgfY%3D%0A&m=UbogYegyhJOd8MD5pXDHVLpkdfH0gvvci5OW50vTexw%3D%0A&s=4da499b672e3e50826f923f340c51cfaa5c79830951ccc3034abd52a1b7402a8
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev@lists.freedesktop.org
>> https://urldefense.proofpoint.com/v1/url?u=http://lists.freedesktop.org/mailman/listinfo/mesa-dev&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=F4msKE2WxRzA%2BwN%2B25muztFm5TSPwE8HKJfWfR2NgfY%3D%0A&m=UbogYegyhJOd8MD5pXDHVLpkdfH0gvvci5OW50vTexw%3D%0A&s=4da499b672e3e50826f923f340c51cfaa5c79830951ccc3034abd52a1b7402a8
>>
_______________________________________________
mesa-dev mailing list
mesa-dev@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/mesa-dev
