From 479da9ea35ae12b4d09462bd0dcae4c41aaece4b Mon Sep 17 00:00:00 2001 From: Konstantinos Margaritis Date: Sun, 30 Apr 2023 18:11:45 +0000 Subject: [PATCH] do proper rounding, handle SH=0 (no rounding for now) --- openpower/sv/twin_butterfly.mdwn | 39 +++++++++++++++++++++----------- 1 file changed, 26 insertions(+), 13 deletions(-) diff --git a/openpower/sv/twin_butterfly.mdwn b/openpower/sv/twin_butterfly.mdwn index aa8048353..534d62194 100644 --- a/openpower/sv/twin_butterfly.mdwn +++ b/openpower/sv/twin_butterfly.mdwn @@ -101,19 +101,32 @@ 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 + prod1 <- MULS(RB, sum)[XLEN:(XLEN*2)-1] + prod2 <- MULS(RB, diff)[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 + 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) + m <- MASK(n, (XLEN-1)) + signbit1 <- prod1[0] + signbit2 <- prod2[0] + smask1 <- ([signbit1]*XLEN) & ¬m + smask2 <- ([signbit2]*XLEN) & ¬m + RT <- (res1 & m | smask1) + RS <- (res2 & m | smask2) ``` Note that if Rc=1 an Illegal Instruction is raised. Rc=1 is `RESERVED` -- 2.30.2