The goal is to implement instructions that calculate the expression:
```
-fdct_round_shift((a +/- b) * c)
+ fdct_round_shift((a +/- b) * c)
```
For the single-coefficient butterfly instruction, and:
```
- fdct_round_shift(a * c1 +/- b * c2)
+ fdct_round_shift(a * c1 +/- b * c2)
```
For the double-coefficient butterfly instruction.
`fdct_round_shift` is defined as `ROUND_POWER_OF_TWO(x, 14)`
```
-#define ROUND_POWER_OF_TWO(value, n) (((value) + (1 << ((n)-1))) >> (n))
+ #define ROUND_POWER_OF_TWO(value, n) (((value) + (1 << ((n)-1))) >> (n))
```
These instructions are at the core of **ALL** FDCT calculations in many major video codecs, including -but not limited to- VP8/VP9, AV1, etc.
The suggestion is to have a single instruction to calculate both values `((a + b) * c) >> N`, and `((a - b) * c) >> N`.
The instruction will run in accumulate mode, so in order to calculate the 2-coeff version one would just have to call the same instruction with different order a, b and a different constant c.
-## [DRAFT] Integer Butterfly Multiply Add/Sub FFT/DCT
+## Integer Butterfly Multiply Add/Sub FFT/DCT
A-Form
+```
+ |0 |6 |11 |16 |21 |26 |31 |
+ | PO | RT | RA | RB | SH | XO |Rc |
+
+```
+
* maddsubrs RT,RA,SH,RB
Pseudo-code:
None
```
-Where we have added this variant in A-Form (defined in fields.txt):
-
-```
-# # 1.6.17 A-FORM
- |0 |6 |11 |16 |21 |26 |31 |
- | PO | RT | RA | RB | SH | XO |Rc |
-
-```
-
-The instruction has been added to `minor_22.csv`:
-
-```
-------01000,ALU,OP_MADDSUBRS,RT,CONST_SH,RB,RT,NONE,CR0,0,0,ZERO,0,NONE,0,0,0,0,1,0,RC_ONLY,0,0,maddsubrs,A,,1,unofficial until submitted and approved/renumbered by the opf isa wg
-```
-
-
# Twin Butterfly Integer DCT Instruction(s)
-## [DRAFT] Floating Twin Multiply-Add DCT [Single]
+## Floating Twin Multiply-Add DCT [Single]
X-Form
CR1 (if Rc=1)
```
-## [DRAFT] Floating Multiply-Add FFT [Single]
+## Floating Multiply-Add FFT [Single]
X-Form