1# mach: bfin 2 3// GENERIC CONVOLUTIONAL ENCODER 4// This a generic rate 1/n convolutional encoder. It computes n output 5// bits for each input bit, based on n generic polynomials. 6// It uses the set of BXOR_CC instructions to compute bit XOR 7// reduction from a state masked by a polynomial. For an alternate 8// solution based on assembling several partial words, as in 9// the BDT benchmark, see file conv_enc.c. The solution presented 10// here is slower than conv_enc.c, but more generic. 11// 12// Forward Shift Register 13// ----------------------- 14// This solution implements the XOR function by shifting the state 15// left by one, applying a mask to the state, and reducing 16// the result with a bit XOR reduction function. 17// ----- XOR------------> G0 18// | | | | 19// +------------------------------+ 20// | b0 b1 b2 b3 b14 b15 | <- in 21// +------------------------------+ 22// | | | | | 23// ----- XOR------------> G1 24// Instruction BXOR computes the bit G0 or G1 and stores it into CC 25// and also into a destination reg half. Here, we take CC and rotate it 26// into an output register. 27// However, one can also store the output bit directly by storing 28// the register half where this bit is placed. This would result 29// in an output structure similar to the one in the original function 30// Convolutional_Encode(), where an entire half word holds a bit. 31// The resulting execution speed would be roughly twice as fast, 32// since there is no need to rotate output bit via CC. 33 34.include "testutils.inc" 35 start 36 37 loadsym P0, input; 38 loadsym P1, output; 39 40 R1 = 0; R2 = 0;R3 = 0; 41 42 R2.L = 0; 43 R2.H = 0xa01d; // polynom 0 44 R3.L = 0; 45 R3.H = 0x12f4; // polynom 1 46 47 // load and CurrentState to upper half of A0 48 A1 = A0 = 0; 49 R0 = 0x0000; 50 A0.w = R0; 51 A0 = A0 << 16; 52 53 // l-loop counter is in P4 54 P4 = 2(Z); 55 // **** START l-LOOP ***** 56l$0: 57 58 // insert 16 bits of input into lower half of A0 59 // and advance input pointer 60 R0 = W [ P0 ++ ] (Z); 61 A0.L = R0.L; 62 63 P5 = 2 (Z); 64 LSETUP ( m$0 , m$0end ) LC0 = P5; // **** BEGIN m-LOOP ***** 65m$0: 66 67 P5 = 8 (Z); 68 LSETUP ( i$1 , i$1end ) LC1 = P5; // **** BEGIN i-LOOP ***** 69i$1: 70 R4.L = CC = BXORSHIFT( A0 , R2 ); // polynom0 -> CC 71 R1 = ROT R1 BY 1; // CC -> R1 72 R4.L = CC = BXOR( A0 , R3 ); // polynom1 -> CC 73i$1end: 74 R1 = ROT R1 BY 1; // CC -> R1 75 76 // store 16 bits of outdata RL1 77m$0end: 78 W [ P1 ++ ] = R1; 79 80 P4 += -1; 81 CC = P4 == 0; 82 IF !CC JUMP l$0; // **** END l-LOOP ***** 83 84 // Check results 85 loadsym I2, output; 86 R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x8c62 ); 87 R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x262e ); 88 R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x5b4d ); 89 R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x834f ); 90 pass 91 92 .data 93input: 94 .dw 0x999f 95 .dw 0x1999 96 97output: 98 .dw 0x0000 99 .dw 0x0000 100 .dw 0x0000 101 .dw 0x0000 102