From 0b538fdd587522928bb7c62a2f303323706b9470 Mon Sep 17 00:00:00 2001 From: Luke Kenneth Casson Leighton Date: Mon, 18 Apr 2022 19:45:02 +0100 Subject: [PATCH] split out SUB_MUL_BORROW into two separate phases one that looks like standard msubx, the other just plain odd --- openpower/sv/bitmanip/divmnu64.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/openpower/sv/bitmanip/divmnu64.c b/openpower/sv/bitmanip/divmnu64.c index 93735d802..44310d32d 100644 --- a/openpower/sv/bitmanip/divmnu64.c +++ b/openpower/sv/bitmanip/divmnu64.c @@ -107,6 +107,7 @@ again: if (rhat < b) goto again; } +#define SUB_MUL_BORROW #ifdef ORIGINAL // Multiply and subtract. k = 0; @@ -124,9 +125,22 @@ again: // Multiply and subtract. uint32_t borrow = 0; + uint32_t phi[2000]; // plenty space + uint32_t plo[2000]; // plenty space + // first, perform mul-and-sub and store in split hi-lo + // this shows the vectorised sv.msubx which stores 128-bit in + // two 64-bit registers for(int i = 0; i <= n; i++) { uint32_t vn_i = i < n ? vn[i] : 0; - uint64_t value = un[i + j] - (uint64_t)qhat * vn_i - borrow; + uint64_t value = un[i + j] - (uint64_t)qhat * vn_i; + plo[i] = value & 0xffffffffLL; + phi[i] = value >> 32; + } + // second, reconstruct the 64-bit result, subtract borrow, + // store top-half (-ve) in new borrow and store low-half as answer + // this is the new (odd) instruction + for(int i = 0; i <= n; i++) { + uint64_t value = (((uint64_t)phi[i]<<32) | plo[i]) - borrow; borrow = -(uint32_t)(value >> 32); un[i + j] = (uint32_t)value; } -- 2.30.2