From: Jacob Lifshay <programmerjake@gmail.com>
Date: Fri, 3 Mar 2023 05:24:22 +0000 (-0800)
Subject: add maddedus to ls003
X-Git-Tag: opf_rfc_ls001_v3~204
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=1b14f6038a6a6524668ba4a4695f35b1eadac9ff;p=libreriscv.git

add maddedus to ls003
---

diff --git a/openpower/sv/rfc/ls003.mdwn b/openpower/sv/rfc/ls003.mdwn
index 05c5aec60..86ccbaac3 100644
--- a/openpower/sv/rfc/ls003.mdwn
+++ b/openpower/sv/rfc/ls003.mdwn
@@ -33,6 +33,7 @@ Instructions added
 
 ```
     maddedu - Multiply-Add Extended Double Unsigned
+    maddedus - Multiply-Add Extended Double Unsigned/Signed
     divmod2du - Divide/Modulo Quad-Double Unsigned
     dsld - Double Shift Left Doubleword
     dsrd - Double Shift Right Doubleword
@@ -175,6 +176,70 @@ maddedu r22,r6,r0,r3
 
 \newpage{}
 
+# Multiply-Add Extended Double Unsigned/Signed
+
+`maddedus RT, RA, RB, RC`
+
+|  0-5  | 6-10 | 11-15 | 16-20 | 21-25 | 26-31 | Form    |
+|-------|------|-------|-------|-------|-------|---------|
+| EXT04 | RT   |  RA   |  RB   |   RC  |  XO   | VA-Form |
+
+Pseudocode:
+
+```
+if (RB)[0] != 0 then                 # workaround no unsigned-signed mul op
+    prod[0:127] <- -((RA) * -(RB))
+else
+    prod[0:127] <- (RA) * (RB)
+sum[0:127] <- prod + EXTS128((RC))
+RT <- sum[64:127]                    # Store low half in RT
+RS <- sum[0:63]                      # RS implicit register, equal to RC
+```
+
+Special registers altered:
+
+    None
+
+The 64-bit operands are (RA), (RB), and (RC).
+(RC) is sign-extended to 128-bits and then summed with the
+128-bit product of zero-extended (RA) and sign-extended (RB).
+The low-order 64 bits of the 128-bit sum are
+placed into register RT.
+The high-order 64 bits of the 128-bit sum are
+placed into register RS.
+RS is implicitly defined as the same register as RC.
+
+*Programmer's Note:
+To achieve a big-integer rolling-accumulation effect:
+assuming the signed scalar to multiply is in r0, and r3 is
+used (effectively) as a 64-bit carry,
+the unsigned vector to multiply by starts at r4 and the signed result vector
+in r20, instructions may be issued `maddedus r20,r4,r0,r3`
+`maddedus r21,r5,r0,r3` etc. where the first `maddedus` will have
+stored the upper half of the 128-bit multiply into r3, such
+that it may be picked up by the second `maddedus`. Repeat inline
+to construct a larger bigint scalar-vector multiply,
+as Scalar GPR register file space permits. If register
+spill is required then r3, as the effective 64-bit carry,
+continues the chain.*
+
+Examples:
+
+```
+# (r0 * r1) + r2, store lower in r4, upper in r2
+maddedus r4, r0, r1, r2
+
+# Chaining together for larger bigint (see Programmer's Note above)
+# r3 starts with zero (no carry-in)
+maddedus r20,r4,r0,r3
+maddedus r21,r5,r0,r3
+maddedus r22,r6,r0,r3
+```
+
+----------
+
+\newpage{}
+
 # Divide/Modulo Quad-Double Unsigned
 
 **Should name be Divide/Module Double Extended Unsigned?**
@@ -389,6 +454,7 @@ XO (26:30)
 |Form| Book | Page | Version | mnemonic | Description |
 |----|------|------|---------|----------|-------------|
 |VA  | I    | #    | 3.2B    |maddedu   | Multiply-Add Extend Double Unsigned |
+|VA  | I    | #    | 3.2B    |maddedus  | Multiply-Add Extend Double Unsigned Signed |
 |VA  | I    | #    | 3.2B    |divmod2du | Divide/Modulo Quad-Double Unsigned |
 |VA2 | I    | #    | 3.2B    |dsld      | Double-Shift Left Doubleword |
 |VA2 | I    | #    | 3.2B    |dsrd      | Double-Shift Right Doubleword |