From fe8e8a47ccde85e7ea4b9d640863c287c875d22a Mon Sep 17 00:00:00 2001 From: lkcl Date: Fri, 7 Feb 2020 16:32:32 +0000 Subject: [PATCH] --- 3d_gpu/architecture/dynamic_simd/add.mdwn | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) create mode 100644 3d_gpu/architecture/dynamic_simd/add.mdwn diff --git a/3d_gpu/architecture/dynamic_simd/add.mdwn b/3d_gpu/architecture/dynamic_simd/add.mdwn new file mode 100644 index 000000000..ec8f3c928 --- /dev/null +++ b/3d_gpu/architecture/dynamic_simd/add.mdwn @@ -0,0 +1,22 @@ +# Partitioned Add + +this principle also applies to subtract and negate (-) + +the basic principle is: the partition bits, when inverted, can actually +be inserted into an (expanded) add, and, if the bit is set, it has +the side-effect of "rolling through" the carry bit of the MSB from +the previous partition. + +this is a really neat trick, basically, that allows the use of a +straight "add" (DSP in an FPGA, add in a simulator) where +otherwise it would be extraordinarily complex, CPU-intensive +and take up large resources. + + partition: .... P... P... P... P... (32 bits) + a : .... .... .... .... .... (32 bits) + b : .... .... .... .... .... (32 bits) + exp-a : ....P....P....P....P.... (32+4 bits, P=1 if no partition) + exp-b : ....0....0....0....0.... (32 bits plus 4 zeros) + exp-o : ....xN...xN...xN...xN... (32+4 bits - x to be discarded) + o : .... N... N... N... N... (32 bits - x ignored, N is carry-over) + -- 2.30.2