From b0cfd6c3c684509ce4700583cef38163d5c810aa Mon Sep 17 00:00:00 2001 From: Konstantinos Margaritis Date: Mon, 1 May 2023 18:30:36 +0000 Subject: [PATCH] working version, need to document limits in precision --- openpower/sv/twin_butterfly.mdwn | 37 ++++++++++++++------------------ 1 file changed, 16 insertions(+), 21 deletions(-) diff --git a/openpower/sv/twin_butterfly.mdwn b/openpower/sv/twin_butterfly.mdwn index 3a78acdab..a2a7b8d7f 100644 --- a/openpower/sv/twin_butterfly.mdwn +++ b/openpower/sv/twin_butterfly.mdwn @@ -105,32 +105,27 @@ Pseudo-code: n <- SH sum <- (RT) + (RA) diff <- (RT) - (RA) - prod1 <- MULS(RB, sum)[XLEN:(XLEN*2)-1] - prod2 <- MULS(RB, diff)[XLEN:(XLEN*2)-1] + prod1 <- MULS(RB, sum) + prod1_lo <- prod1[XLEN:(XLEN*2)-1] + prod2 <- MULS(RB, diff) + prod2_lo <- prod2[XLEN:(XLEN*2)-1] if n = 0 then - #round <- EXTS([0]*(XLEN-1) || [1]*1) - #prod1 <- ROTL64(prod1, 1) - #prod2 <- ROTL64(prod2, 1) - #prod1 <- prod1 + round - #prod2 <- prod2 + round - #res1 <- ROTL64(prod1, XLEN-1) - #res2 <- ROTL64(prod2, XLEN-1) - #m <- MASK(1, (XLEN-1)) - RT <- prod1 - RS <- prod2 + RT <- prod1_lo + RS <- prod2_lo else - round <- EXTS([0]*(XLEN -n -1) || [1]*1 || [0]*(n-1)) - prod1 <- prod1 + round - prod2 <- prod2 + round - res1 <- ROTL64(prod1, XLEN-n) - res2 <- ROTL64(prod2, XLEN-n) + round <- [0]*XLEN + round[XLEN -n] <- 1 + prod1_lo <- prod1_lo + round + prod2_lo <- prod2_lo + round m <- MASK(n, (XLEN-1)) - signbit1 <- prod1[0] - signbit2 <- prod2[0] + res1 <- ROTL64(prod1_lo, XLEN-n) & m + res2 <- ROTL64(prod2_lo, XLEN-n) & m + signbit1 <- prod1_lo[0] + signbit2 <- prod2_lo[0] smask1 <- ([signbit1]*XLEN) & ¬m smask2 <- ([signbit2]*XLEN) & ¬m - RT <- (res1 & m | smask1) - RS <- (res2 & m | smask2) + RT <- (res1 | smask1) + RS <- (res2 | smask2) ``` Note that if Rc=1 an Illegal Instruction is raised. Rc=1 is `RESERVED` -- 2.30.2