* [[openpower/isa/svfparith]]
* [[openpower/isa/svfixedarith]]
* [[openpower/sv/rfc/ls016]]
-
<!-- show -->
+Although best used with SVP64 REMAP these instructions may be used in a Scalar-only
+context to save considerably on DCT, DFT and FFT processing. Whilst some hardware
+implementations may not necessarily implement them efficiently (slower Micro-coding)
+savings still come from the reduction in temporary registers as well as instruction
+count.
+
# Rationale for Twin Butterfly Integer DCT Instruction(s)
The number of general-purpose uses for DCT is huge. The number of
For the double-coefficient butterfly instruction.
-`fdct_round_shift` is defined as `ROUND_POWER_OF_TWO(x, 14)`
+In a 32-bit context `fdct_round_shift` is defined as `ROUND_POWER_OF_TWO(x, 14)`
```
#define ROUND_POWER_OF_TWO(value, 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.
-Arm includes special instructions to optimize these operations, although
+ARM includes special instructions to optimize these operations, although
they are limited in precision: `vqrdmulhq_s16`/`vqrdmulhq_s32`.
The suggestion is to have a single instruction to calculate both values
b and a different constant c.
Example taken from libvpx
-<https://chromium.googlesource.com/webm/libvpx/+/refs/heads/main/vpx_dsp/fwd_txfm.c#132>:
+<https://chromium.googlesource.com/webm/libvpx/+/refs/tags/v1.13.0/vpx_dsp/fwd_txfm.c#132>:
```
#include <stdint.h>
```
|0 |6 |11 |16 |21 |26 |31 |
| PO | RT | RA | RB | SH | XO |Rc |
-
```
-* maddsubrs RT,RA,SH,RB
+* maddsubrs RT,RA,RB,SH
Pseudo-code:
```
n <- SH
- sum <- (RT) + (RA)
- diff <- (RT) - (RA)
- prod1 <- MULS(RB, sum)[XLEN:(XLEN*2)-1] + 1
- prod2 <- MULS(RB, diff)[XLEN:(XLEN*2)-1] + 1
- res1 <- ROTL64(prod1, XLEN-n)
- res2 <- ROTL64(prod2, XLEN-n)
- m <- MASK(n, (XLEN-1))
- signbit1 <- res1[0]
- signbit2 <- res2[0]
- smask1 <- ([signbit1]*XLEN) & ¬m
- smask2 <- ([signbit2]*XLEN) & ¬m
- s64_1 <- [0]*(XLEN-1) || signbit1
- s64_2 <- [0]*(XLEN-1) || signbit2
- RT <- (res1 & m | smask1) + s64_1
- RS <- (res2 & m | smask2) + s64_2
+ sum <- (RT[0] || RT) + (RA[0] || RA)
+ diff <- (RT[0] || RT) - (RA[0] || RA)
+ prod1 <- MULS(RB, sum)
+ prod2 <- MULS(RB, diff)
+ if n = 0 then
+ prod1_lo <- prod1[XLEN+1:(XLEN*2)]
+ prod2_lo <- prod2[XLEN+1:(XLEN*2)]
+ RT <- prod1_lo
+ RS <- prod2_lo
+ else
+ round <- [0]*(XLEN*2 + 1)
+ round[XLEN*2 - n + 1] <- 1
+ prod1 <- prod1 + round
+ prod2 <- prod2 + round
+ res1 <- prod1[XLEN - n + 1:XLEN*2 - n]
+ res2 <- prod2[XLEN - n + 1:XLEN*2 - n]
+ RT <- res1
+ RS <- res2
```
-Note that if Rc=1 an Illegal Instruction is raised. Rc=1 is `RESERVED`
-
Similar to `RTp`, this instruction produces an implicit result, `RS`,
which under Scalar circumstances is defined as `RT+1`. For SVP64 if
`RT` is a Vector, `RS` begins immediately after the Vector `RT` where
None
```
+# [DRAFT] Integer Butterfly Multiply Add and Round Shift FFT/DCT
+
+A-Form
+
+* maddrs RT,RA,RB,SH
+
+Pseudo-code:
+
+```
+ n <- SH
+ prod <- MULS(RB, RA)
+ if n = 0 then
+ prod_lo <- prod[XLEN:(XLEN*2) - 1]
+ RT <- (RT) + prod_lo
+ else
+ res[0:XLEN*2-1] <- (EXTSXL((RT)[0], 1) || (RT)) + prod
+ round <- [0]*XLEN*2
+ round[XLEN*2 - n] <- 1
+ res <- res + round
+ RT <- res[XLEN - n:XLEN*2 - n -1]
+```
+
+Special Registers Altered:
+
+ None
+
+# [DRAFT] Integer Butterfly Multiply Sub and Round Shift FFT/DCT
+
+A-Form
+
+* msubrs RT,RA,RB,SH
+
+Pseudo-code:
+
+```
+ n <- SH
+ prod <- MULS(RB, RA)
+ if n = 0 then
+ prod_lo <- prod[XLEN:(XLEN*2) - 1]
+ RT <- (RT) - prod_lo
+ else
+ res[0:XLEN*2-1] <- (EXTSXL((RT)[0], 1) || (RT)) - prod
+ round <- [0]*XLEN*2
+ round[XLEN*2 - n] <- 1
+ res <- res + round
+ RT <- res[XLEN - n:XLEN*2 - n -1]
+```
+
+Special Registers Altered:
+
+ None
+
+
+This pair of instructions is supposed to be used in complement to the maddsubrs
+to produce the double-coefficient butterfly instruction. In order for that
+to work, instead of passing c2 as coefficient, we have to pass c2-c1 instead.
+
+In essence, we are calculating the quantity `a * c1 +/- b * c1` first, with
+`maddsubrs` *without* shifting (so `SH=0`) and then we add/sub `b * (c2-c1)`
+from the previous `RT`, and *then* do the shifting.
+
+In the following example, assume `a` in `R1`, `b` in `R10`, `c1` in `R11` and `c2 - c1` in `R12`.
+The first instruction will put `a * c1 + b * c1` in `R1` (`RT`), `a * c1 - b * c1` in `RS`
+(here, `RS = RT +1`, so `R2`).
+Then, `maddrs` will add `b * (c2 - c1)` to `R1` (`RT`), and `msubrs` will subtract it from `R2` (`RS`), and then
+round shift right both quantities 14 bits:
+
+```
+ maddsubrs 1,10,0,11
+ maddrs 1,10,12,14
+ msubrs 2,10,12,14
+```
+
+In scalar code, that would take ~16 instructions for both operations.
+
-------
\newpage{}
-# Twin Butterfly Floating-Point DCT Instruction(s)
+# Twin Butterfly Floating-Point DCT and FFT Instruction(s)
**Add the following to Book I Section 4.6.6.3**
Using the exact same operand input register values from FRT and FRB
that were used to create FRS, the Floating-Point operand in register
FRB is subtracted from the floating-point operand in register FRT and
-the result then multiplied by FRA to create an intermediate result that
-is stored in FRT.
+the result then rounded before being multiplied by FRA to create an
+intermediate result that is stored in FRT.
The add into FRS is treated exactly as `fadds`. The creation of the
-result FRT is **not** the same as that of `fmsubs`.
-The creation of FRS and FRT are treated as parallel independent operations
-which occur at the same time.
+result FRT is **not** the same as that of `fmsubs`, but is instead as if
+`fsubs` were performed first followed by `fmuls`. The creation of FRS
+and FRT are treated as parallel independent operations which occur at
+the same time.
Note that if Rc=1 an Illegal Instruction is raised. Rc=1 is `RESERVED`
Using the exact same values of FRT, FRT and FRB as used to create
FRS, the floating-point operand in register FRT is multiplied by the
-floating-point operand in register FRA. The float- ing-point operand
+floating-point operand in register FRA. The floating-point operand
in register FRB is subtracted from this intermediate result, and the
intermediate stored in FRT.
Vector `FRT` where the length of `FRT` is set by `SVSTATE.MAXVL`
(Max Vector Length).
-
Special Registers Altered:
```
FX OX UX XX
VXSNAN VXISI VXIMZ
```
+
## Floating-Point Twin Multiply-Add DCT
X-Form
Using the exact same operand input register values from FRT and FRB
that were used to create FRS, the Floating-Point operand in register
FRB is subtracted from the floating-point operand in register FRT and
-the result then multiplied by FRA to create an intermediate result that
-is stored in FRT.
+the result then rounded before being multiplied by FRA to create an
+intermediate result that is stored in FRT.
The add into FRS is treated exactly as `fadd`. The creation of the
-result FRT is **not** the same as that of `fmsub`.
-The creation of FRS and FRT are treated as parallel independent operations
-which occur at the same time.
+result FRT is **not** the same as that of `fmsub`, but is instead as if
+`fsub` were performed first followed by `fmuls. The creation of FRS
+and FRT are treated as parallel independent operations which occur at
+the same time.
Note that if Rc=1 an Illegal Instruction is raised. Rc=1 is `RESERVED`
```
-## [DRAFT] Floating-Point Add FFT/DCT [Single]
+## Floating-Point Add FFT/DCT [Single]
A-Form
+```
+ |0 |6 |11 |16 |21 |26 |31 |
+ | PO | FRT | FRA | FRB | / | XO |Rc |
+```
+
* ffadds FRT,FRA,FRB (Rc=0)
-* ffadds. FRT,FRA,FRB (Rc=1)
Pseudo-code:
FPRF FR FI
FX OX UX XX
VXSNAN VXISI
- CR1 (if Rc=1)
```
-## [DRAFT] Floating-Point Add FFT/DCT [Double]
+## Floating-Point Add FFT/DCT [Double]
A-Form
+```
+ |0 |6 |11 |16 |21 |26 |31 |
+ | PO | FRT | FRA | FRB | / | XO |Rc |
+```
+
* ffadd FRT,FRA,FRB (Rc=0)
-* ffadd. FRT,FRA,FRB (Rc=1)
Pseudo-code:
FPRF FR FI
FX OX UX XX
VXSNAN VXISI
- CR1 (if Rc=1)
```
-## [DRAFT] Floating-Point Subtract FFT/DCT [Single]
+## Floating-Point Subtract FFT/DCT [Single]
A-Form
+```
+ |0 |6 |11 |16 |21 |26 |31 |
+ | PO | FRT | FRA | FRB | / | XO |Rc |
+```
+
* ffsubs FRT,FRA,FRB (Rc=0)
-* ffsubs. FRT,FRA,FRB (Rc=1)
Pseudo-code:
FPRF FR FI
FX OX UX XX
VXSNAN VXISI
- CR1 (if Rc=1)
```
-## [DRAFT] Floating-Point Subtract FFT/DCT [Double]
+## Floating-Point Subtract FFT/DCT [Double]
A-Form
+```
+ |0 |6 |11 |16 |21 |26 |31 |
+ | PO | FRT | FRA | FRB | / | XO |Rc |
+```
+
* ffsub FRT,FRA,FRB (Rc=0)
-* ffsub. FRT,FRA,FRB (Rc=1)
Pseudo-code:
FPRF FR FI
FX OX UX XX
VXSNAN VXISI
- CR1 (if Rc=1)
```
projects / libreriscv.git / blobdiff