remove autogen code, add rationale

diff --git a/openpower/sv/twin_butterfly.mdwn b/openpower/sv/twin_butterfly.mdwn
index 063671fec649b0c957964dea7503ee6c6cc44785..da1a70bd519f915450bae123a9f30ed8800d7552 100644 (file)
--- a/openpower/sv/twin_butterfly.mdwn
+++ b/openpower/sv/twin_butterfly.mdwn
@@ -25,6 +25,9 @@ For the double-coefficient butterfly instruction.
 #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.
+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 `((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.
 
@@ -61,24 +64,6 @@ Where BF-Form is defined in fields.txt:
 
 ```
 
-The resulting autogenerated code is:
-
-```
-class butterfly:
-    @inject()
-    def op_maddsubrs(self, RA, RB, RC, RT):
-        RT2 = copy_assign_rhs(RT + 1)
-        sum = copy_assign_rhs(RA + RB)
-        diff = copy_assign_rhs(RA - RB)
-        prod1 = copy_assign_rhs(self.MUL(RC, sum))
-        prod2 = copy_assign_rhs(self.MUL(RC, diff))
-        res1 = copy_assign_rhs(self.ROTL64(prod1, SH))
-        res2 = copy_assign_rhs(self.ROTL64(prod2, SH))
-        RT = copy_assign_rhs(RT + res1)
-        RT2 = copy_assign_rhs(RT2 + res2)
-        return (RT,)
-```
-
 The instruction has been added to `minor_59.csv`:
 ```
 1111011111,ALU,OP_MADDSUBRS,RA,RB,RC,RT,NONE,CR1,0,0,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