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[/] [forwardcom/] [trunk/] [subfunctions.vh] - Rev 24
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////////////////////////////////////////////////////////////////////////////////// // Engineer: Agner Fog // // Create Date: 2020-06-13 // Last modified: 2021-08-03 // Module Name: subfunctions // Project Name: ForwardCom soft core // Target Devices: Artix 7 // Tool Versions: Vivado v. 2020.1 // License: CERN-OHL-W v. 2 or later // Description: Subfunctions for calculations: // bitscan: find highest set bit // popcount: count number of 1-bits // reversebits: reverse order of bits // truth_table_lookup: 3-input truth table ////////////////////////////////////////////////////////////////////////////////// `include "defines.vh" // 6-input popcount, fits into 6-input LUT. function [2:0] popcount6; input [5:0] inp; integer sum; sum = 0; for (integer k = 0; k < 6; k ++) begin sum += {2'b00, inp[k]}; end return sum; endfunction // 32 input popcount function [5:0] popcount32; input [31:0] inp; logic[5:0] sum; sum = 0; for (integer j = 0; j < 5; j++) begin sum += popcount6(inp[(j*6)+:6]); end sum += popcount6({4'b0,inp[31:30]}); return sum; endfunction // 64 input popcount function [6:0] popcount64; input [63:0] inp; logic[6:0] sum; sum = 0; for (integer j = 0; j < 10; j++) begin sum += popcount6(inp[(j*6)+:6]); end sum += popcount6({2'b0,inp[63:60]}); return sum; endfunction // 64 input bit scan // (also known as leading zero counter or priority encoder) // return value: // bitscan64[6:1] is an index to the highest 1-bit in the input // bitscan64[0] is 1 if all input bits are zero function [6:0] bitscan64A; input [63:0] m0; // 64 bits input logic [5:0] r; // index to highest 1-bit logic iszero; // indicates that input is zero logic [15:0] m1; // subdivision logic [3:0] m2; // subdivision r = 0; // divide into four blocks of 16 bits each if (|m0[63:48]) begin r[5:4] = 3; // r[5:4] indicates which 16-bit block contains the highest 1-bit m1 = m0[63:48]; // m1 is the 16-bit block that contains the highest 1-bit end else if (|m0[47:32]) begin r[5:4] = 2; m1 = m0[47:32]; end else if (|m0[31:16]) begin r[5:4] = 1; m1 = m0[31:16]; end else begin r[5:4] = 0; m1 = m0[15:0]; end // now subdivide m1 into four blocks of 4 bits each if (|m1[15:12]) begin r[3:2] = 3; // r[3:2] indicates which 4-bit block of m1 contains the highest 1-bit m2 = m1[15:12]; // m2 is the 4-bit block that contains the highest 1-bit end else if (|m1[11:8]) begin m2 = m1[11:8]; r[3:2] = 2; end else if (|m1[7:4]) begin m2 = m1[7:4]; r[3:2] = 1; end else begin m2 = m1[3:0]; r[3:2] = 0; end // finally, test each of the four bits in m2 if (m2[3]) r[1:0] = 3; // r[1:0] indicates which of the 4 bit bits in m2 contains the highest 1-bit else if (m2[2]) r[1:0] = 2; else if (m2[1]) r[1:0] = 1; else r[1:0] = 0; // test if everything is zero iszero = ~|m2; // return two values return {r, iszero}; endfunction // 64 input bit scan, alternative implementation // (this one is slightly slower) // return value: // bitscan64[6:1] is an index to the highest 1-bit in the input // bitscan64[0] is 1 if all input bits are zero function [6:0] bitscan64B; input [63:0] m0; // 64 bits input logic [5:0] r; // index to highest 1-bit logic iszero; // indicates that input is zero logic [3:0] m1; // subdivision flags logic [3:0] m2; // subdivision r = 0; if (|m0[63:48]) begin r[5:4] = 3; m1[3] = |m0[63:60]; m1[2] = |m0[59:56]; m1[1] = |m0[55:52]; m1[0] = |m0[51:48]; end else if (|m0[47:32]) begin r[5:4] = 2; m1[3] = |m0[47:44]; m1[2] = |m0[43:40]; m1[1] = |m0[39:36]; m1[0] = |m0[35:32]; end else if (|m0[31:16]) begin r[5:4] = 1; m1[3] = |m0[31:28]; m1[2] = |m0[27:24]; m1[1] = |m0[23:20]; m1[0] = |m0[19:16]; end else begin r[5:4] = 0; m1[3] = |m0[15:12]; m1[2] = |m0[11:8]; m1[1] = |m0[7:4]; m1[0] = |m0[3:0]; end if (m1[3]) begin r[3:2] = 3; end else if (m1[2]) begin r[3:2] = 2; end else if (m1[1]) begin r[3:2] = 1; end else begin r[3:2] = 0; end // extract the 4-bit block that contains the highest 1-bit m2 = m0[{r[5:2],2'b0}+: 4]; if (m2[3]) r[1:0] = 3; else if (m2[2]) r[1:0] = 2; else if (m2[1]) r[1:0] = 1; else r[1:0] = 0; // test if everything is zero iszero = ~|m2; // return two values return {r, iszero}; endfunction // 64 input bit scan, alternative implementation // (this one appears to be the fastest) // return value: // bitscan64[6:1] is an index to the highest 1-bit in the input // bitscan64[0] is 1 if all input bits are zero function [6:0] bitscan64C; input [63:0] m0; // 64 bits input logic [5:0] r; // index to highest 1-bit logic iszero; // indicates that input is zero logic [15:0] m1; // subdivision flags logic [3:0] m2; // subdivision logic [3:0] m3; // subdivision r = 0; m1[15] = |m0[63:60]; m1[14] = |m0[59:56]; m1[13] = |m0[55:52]; m1[12] = |m0[51:48]; m1[11] = |m0[47:44]; m1[10] = |m0[43:40]; m1[9] = |m0[39:36]; m1[8] = |m0[35:32]; m1[7] = |m0[31:28]; m1[6] = |m0[27:24]; m1[5] = |m0[23:20]; m1[4] = |m0[19:16]; m1[3] = |m0[15:12]; m1[2] = |m0[11:8]; m1[1] = |m0[7:4]; m1[0] = |m0[3:0]; m2[3] = |m1[15:12]; m2[2] = |m1[11:8]; m2[1] = |m1[7:4]; m2[1] = |m1[3:0]; if (m2[3]) begin r[5:4] = 3; if (m1[15]) r[3:2] = 3; else if (m1[14]) r[3:2] = 2; else if (m1[13]) r[3:2] = 1; else r[3:2] = 0; end else if (m2[2]) begin r[5:4] = 2; if (m1[11]) r[3:2] = 3; else if (m1[10]) r[3:2] = 2; else if (m1[9]) r[3:2] = 1; else r[3:2] = 0; end else if (m2[1]) begin r[5:4] = 1; if (m1[7]) r[3:2] = 3; else if (m1[6]) r[3:2] = 2; else if (m1[5]) r[3:2] = 1; else r[3:2] = 0; end else begin r[5:4] = 0; if (m1[3]) r[3:2] = 3; else if (m1[2]) r[3:2] = 2; else if (m1[1]) r[3:2] = 1; else r[3:2] = 0; end // extract the 4-bit block that contains the highest 1-bit m3 = m0[{r[5:2],2'b0}+: 4]; if (m3[3]) r[1:0] = 3; else if (m3[2]) r[1:0] = 2; else if (m3[1]) r[1:0] = 1; else r[1:0] = 0; // test if everything is zero iszero = ~|m2; // return two values return {r, iszero}; endfunction // This function finds the index to a single bit in a 64-bit input // where only one bit is set. Used when bitscan relies on the output of roundp2 // Use the formula b = a & ~(a-1) to isolate the lowest set bit before // calling bitindex. Reverse the order of the bits to find the highest set bit. // The return value is {r, iszero} where r is the position of the single 1-bit, // iszero is 1 if all input bits are zero. // Note that this function does not work if more than one input bit is 1. function [6:0] bitindex; input [63:0] m0; // 64 bits input logic [5:0] r; // index to highest 1-bit logic iszero; // indicates that input is zero logic [15:0] m2; // OR combination of groups of four bits m2[15] = |m0[63:60]; m2[14] = |m0[59:56]; m2[13] = |m0[55:52]; m2[12] = |m0[51:48]; m2[11] = |m0[47:44]; m2[10] = |m0[43:40]; m2[9] = |m0[39:36]; m2[8] = |m0[35:32]; m2[7] = |m0[31:28]; m2[6] = |m0[27:24]; m2[5] = |m0[23:20]; m2[4] = |m0[19:16]; m2[3] = |m0[15:12]; m2[2] = |m0[11:8]; m2[1] = |m0[7:4]; m2[0] = 0;//|m0[3:0]; // not used r[5] = m2[8]|m2[9]|m2[10]|m2[11]|m2[12]|m2[13]|m2[14]|m2[15]; r[4] = m2[4]|m2[5]|m2[6]|m2[7]|m2[12]|m2[13]|m2[14]|m2[15]; r[3] = m2[2]|m2[3]|m2[6]|m2[7]|m2[10]|m2[11]|m2[14]|m2[15]; r[2] = m2[1]|m2[3]|m2[5]|m2[7]|m2[9]|m2[11]|m2[13]|m2[15]; r[1] = m0[2]|m0[3]|m0[6]|m0[7]|m0[10]|m0[11]|m0[14]|m0[15]| m0[18]|m0[19]|m0[22]|m0[23]|m0[26]|m0[27]|m0[30]|m0[31]| m0[34]|m0[35]|m0[38]|m0[39]|m0[42]|m0[43]|m0[46]|m0[47]| m0[50]|m0[51]|m0[54]|m0[55]|m0[58]|m0[59]|m0[62]|m0[63]; r[0] = m0[1]|m0[3]|m0[5]|m0[7]|m0[9]|m0[11]|m0[13]|m0[15]| m0[17]|m0[19]|m0[21]|m0[23]|m0[25]|m0[27]|m0[29]|m0[31]| m0[33]|m0[35]|m0[37]|m0[39]|m0[41]|m0[43]|m0[45]|m0[47]| m0[49]|m0[51]|m0[53]|m0[55]|m0[57]|m0[59]|m0[61]|m0[63]; iszero = (~|r) && ~(m0[0]); // return two values return {r, iszero}; endfunction // reverse order of bits function [7:0] reversebits8; input [7:0] in; // 8 bits input return {in[0],in[1],in[2],in[3],in[4],in[5],in[6],in[7]}; endfunction // reverse order of bits function [15:0] reversebits16; input [15:0] in; // 16 bits input return {reversebits8(in[7:0]),reversebits8(in[15:8])}; endfunction // reverse order of bits function [31:0] reversebits32; input [31:0] in; // 32 bits input return {reversebits8(in[7:0]),reversebits8(in[15:8]),reversebits8(in[23:16]),reversebits8(in[31:24])}; endfunction // reverse order of bits function [63:0] reversebits64; input [63:0] in; // 32 bits input return {reversebits8(in[7:0]),reversebits8(in[15:8]),reversebits8(in[23:16]),reversebits8(in[31:24]), reversebits8(in[39:32]),reversebits8(in[47:40]),reversebits8(in[55:48]),reversebits8(in[63:56])}; endfunction // Truth table lookup with three inputs for truth_tab3 instruction function [`RB1:0] truth_table_lookup; input [`RB1:0] in1; // input 1 input [`RB1:0] in2; // input 2 input [`RB1:0] in3; // input 3 input [7:0] ttable; // 8 bit truth table logic [`RB1:0] res; // result for (integer k = 0; k < `RB; k++) begin // loop through bits res[k] = ttable[{in3[k],in2[k],in1[k]}]; // lookup with 3 bits index end truth_table_lookup = res;// result endfunction
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