add ls001.po9 RFC

[libreriscv.git] / openpower / sv / twin_butterfly.mdwn

diff --git a/openpower/sv/twin_butterfly.mdwn b/openpower/sv/twin_butterfly.mdwn
index 7aa8f3200dca54e2c268200542ee11cc2adc7e4a..32a968914925f0a0579e364fd411f83b40b47ec7 100644 (file)
--- a/openpower/sv/twin_butterfly.mdwn
+++ b/openpower/sv/twin_butterfly.mdwn
@@ -2,8 +2,9 @@
 * <https://libre-soc.org/openpower/sv/biginteger/> for format and
   information about implicit RS/FRS
 * <https://git.libre-soc.org/?p=openpower-isa.git;a=blob;f=src/openpower/decoder/isa/test_caller_svp64_dct.py;hb=HEAD>
+* [[openpower/isa/svfparith]]
 
-# [DRAFT] Twin Butterfly DCT Instruction(s)
+# Twin Butterfly Integer DCT Instruction(s)
 
 The goal is to implement instructions that calculate the expression:
 
@@ -31,42 +32,110 @@ Arm includes special instructions to optimize these operations, although they ar
 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
+## [DRAFT] Integer Butterfly Multiply Add/Sub FFT/DCT
 
-BF-Form
+A-Form
 
-* maddsubrs  RT,RA,RB,RC,SH
+* maddsubrs  RT,RA,SH,RB
 
 Pseudo-code:
 
-    RT2 <- RT + 1
-    sum <- (RA) + (RB)
-    diff <- (RA) - (RB)
-    prod1 <- MUL(RC, sum)
-    prod2 <- MUL(RC, diff)
-    res1 <- ROTL64(prod1, SH)
-    res2 <- ROTL64(prod2, SH)
-    RT <- (RT) + res1
-    RT2 <- (RT2) + res2
+```
+    n <- SH
+    sum <- (RT) + (RA)
+    diff <- (RT) - (RA)
+    prod1 <- MULS(RB, sum)[XLEN:(XLEN*2)-1]
+    prod2 <- MULS(RB, diff)[XLEN:(XLEN*2)-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
+```
 
 Special Registers Altered:
 
+```
     None
 ```
 
-Where BF-Form is defined in fields.txt:
+Where we have added this variant in A-Form (defined in fields.txt):
 
 ```
-# 1.6.39 BF-FORM
-    |0     | 6   |11   |16   |21   | 26 |27  31|
-    | PO   | RT  | RA  | RB  | RC  | SH | XO   |
+# # 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,RA,RB,RC,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
+------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]
+
+X-Form
+
 ```
+    |0     |6     |11      |16     |21      |31 |
+    | PO   |  FRT |  FRA   |  FRB  |   XO   | Rc|
+```
+
+* fdmadds FRT,FRA,FRB (Rc=0)
+* fdmadds. FRT,FRA,FRB (Rc=1)
+
+Pseudo-code:
+
+```
+    FRS <- FPADD32(FRT, FRB)
+    sub <- FPSUB32(FRT, FRB)
+    FRT <- FPMUL32(FRA, sub)
+```
+
+Special Registers Altered:
 
+```
+    FPRF FR FI
+    FX OX UX XX
+    VXSNAN VXISI VXIMZ
+    CR1          (if Rc=1)
+```
+
+## [DRAFT] Floating Multiply-Add FFT [Single]
+
+X-Form
+
+```
+    |0     |6     |11      |16     |21      |31 |
+    | PO   |  FRT |  FRA   |  FRB  |   XO   | Rc|
+```
+
+* ffmadds FRT,FRA,FRB (Rc=0)
+* ffmadds. FRT,FRA,FRB (Rc=1)
+
+Pseudo-code:
+
+```
+    FRS <- FPMULADD32(FRT, FRA, FRB, -1, 1)
+    FRT <- FPMULADD32(FRT, FRA, FRB, 1, 1)
+```
+
+Special Registers Altered:
+
+```
+    FPRF FR FI
+    FX OX UX XX
+    VXSNAN VXISI VXIMZ
+    CR1          (if Rc=1)
+```