#include <L1Trigger/L1TCalorimeter/src/firmware/CordicXilinx.cc>

Public Member Functions
	CordicXilinx (int inputBits, int outputBits, bool debug=false)

int	encodeAngle (const double angleFloat) const

void	operator() (int32_t xInput, int32_t yInput, int32_t &aPhi, uint32_t &aMagnitude) const

Private Types
enum	{ Pi, HalfPi, NHalfPi }

Private Attributes
const bool	debug_

std::array< int, 3 >	encodedAngles_

const int	inputBits_

int	internalBits_

int	iterations_

const int	outputBits_

std::vector< int >	rotations_

int	scaleFactor_

Detailed Description

Description: Emulates parts of the Xilinx DSP IP CORDIC routine, as described in http://www.xilinx.com/support/documentation/ip_documentation/cordic/v6_0/pg105-cordic.pdf This class only implements the vector translation, returning magnitude and phase, given signed x and y inputs. The inputs and outputs are not packed, so that normal signed integer arithmetic works as expected. They can easily be packed into a fixed width by abs() and placing a sign bit at the appropriate offset. The applicable configuration parameters that are being emulated are the following:

Functional Selection: Translate
Phase Format: Radians
Round Mode: Truncate
Advanced Configuration Parameters: Iterations=0, Precision=0, Coarse Rotation, Compensation Scaling = Embedded Multiplier In addition, an arbitrary input and output width can be specified, HOWEVER, only in=24, out=19 has been rigorously tested against the Xilinx proprietary emulator.

Tests: Full circle at various magnitudes, including maximum; a few billion random inputs Limited hardware comparisons have shown agreement as well. Test framework: https://github.com/nsmith-/cordic_test

Original Author: Nick Smith ( nick..nosp@m.smit.nosp@m.h@cer.nosp@m.n.ch )

Definition at line 8 of file CordicXilinx.h.

Member Enumeration Documentation

anonymous enum

private

Enumerator
Pi
HalfPi
NHalfPi

Definition at line 30 of file CordicXilinx.h.

30 { Pi, HalfPi, NHalfPi };

CordicXilinx::Pi

Definition: CordicXilinx.h:30

CordicXilinx::NHalfPi

Definition: CordicXilinx.h:30

CordicXilinx::HalfPi

Definition: CordicXilinx.h:30

Constructor & Destructor Documentation

CordicXilinx::CordicXilinx	(	int	inputBits,
		int	outputBits,
		bool	debug = `false`
	)

Definition at line 34 of file CordicXilinx.cc.

References debug_, encodeAngle(), encodedAngles_, HalfPi, mps_fire::i, internalBits_, iterations_, cmsBatch::log, M_PI, NHalfPi, Pi, funct::pow(), idealTransformation::rotation, rotations_, JetEnergyShift_cfi::scaleFactor, and scaleFactor_.

                                                                     :
     inputBits_(inputBits),
     outputBits_(outputBits),
     debug_(debug)
 {
     // Coarse rotation lowers necessary iterations by 2
     iterations_ = outputBits-2;
     // Internal precision is by default this value (when set to 0 in xilinx config)
     internalBits_ = outputBits+ceil(log((float) iterations_)/log(2.));
 
     double scaleFactor = 1.;
     for(int i=1; i<=iterations_; ++i)
     {
         int rotation = encodeAngle(atan(pow(2.,-i)));
         rotations_.push_back(rotation);
         scaleFactor *= pow(1+pow(2.,-2*i), -0.5);
     }
     scaleFactor_ = scaleFactor*pow(2., internalBits_-1)+0.5;
     
     // Precompute angles table for speed
     encodedAngles_[Pi] = encodeAngle(M_PI);
     encodedAngles_[HalfPi] = encodeAngle(M_PI/2);
     encodedAngles_[NHalfPi] = encodeAngle(-M_PI/2);
 
     if ( debug_ ) printf("Cordic setup: %d iterations, %d internal bits, scale factor = %d\n", iterations_, internalBits_, scaleFactor_);
 }

Member Function Documentation

int CordicXilinx::encodeAngle ( const double angleFloat ) const

Definition at line 61 of file CordicXilinx.cc.

References internalBits_, M_PI, and funct::pow().

Referenced by CordicXilinx().

 {
     assert(fabs(angleFloat)<=M_PI);
     // Xilinx seems to store rounded rotation table
     return angleFloat*pow(2., internalBits_-3)+0.5;
 }

void CordicXilinx::operator()	(	int32_t	xInput,
		int32_t	yInput,
		int32_t &	aPhi,
		uint32_t &	aMagnitude
	)		const

Definition at line 68 of file CordicXilinx.cc.

References funct::abs(), gather_cfg::cout, debug_, encodedAngles_, HalfPi, mps_fire::i, inputBits_, internalBits_, iterations_, NHalfPi, outputBits_, Pi, funct::pow(), idealTransformation::rotation, rotations_, scaleFactor_, Validation_hcalonly_cfi::sign, x, and y.

 {
     // Assumption in algorithm is that arithmetic shifts are used for ints (as opposed to logical shifts)
     static_assert( ((int) -1)>>3 == (int) -1 , "Signed ints need to use arithmetic shifts for this algorithm to work properly!");
 
     // Input checks
     // Input is in 2QN format, and for xilinx
     // the max is +- 1.0000...
     assert(abs(xInput) <= (1<<(inputBits_-1)));
     assert(abs(yInput) <= (1<<(inputBits_-1)));
     
     // Rotation to get from current vector to origin
     // must invert to get aPhi
     int rotation(0);
     int x,y;
 
     // Debug tool
     auto printVals = [&x,&y,&rotation,this]
     {
         printf("x: % 8d y: % 8d phi: % 8d outphi: % 8d float phi = % f\n",
             x,
             y,
             rotation,
             (abs(rotation)>>(internalBits_-outputBits_)) * ((rotation>0) ? -1:1),
             rotation/pow(2., internalBits_-3)
         );
     };
 
     // Convert to internal precision
     if ( internalBits_ > inputBits_ )
     {
         x = xInput << (internalBits_-inputBits_);
         y = yInput << (internalBits_-inputBits_);
     }
     else
     {
         x = xInput >> (inputBits_-internalBits_);
         y = yInput >> (inputBits_-internalBits_);
     }
     if ( debug_ ) printVals();
 
     // Coarse rotate to [-pi/4,pi/4)
     if ( x-y >= 0 )
     {
         if ( x+y >= 0 )
         {
             // East (Correct) quadrant
         }
         else
         {
             // South, rotate by +pi/2
             int xtmp = -y;
             int ytmp = x;
             x = xtmp;
             y = ytmp;
             rotation += encodedAngles_[HalfPi];
         }
     }
     else
     {
         if ( x+y >= 0 )
         {
             // North, rotate by -pi/2
             int xtmp = y;
             int ytmp = -x;
             x = xtmp;
             y = ytmp;
             rotation += encodedAngles_[NHalfPi];
         }
         else
         {
             // West, rotate by pi
             x = -x;
             y = -y;
             rotation += encodedAngles_[Pi];
         }
     }
     if ( debug_ ) std::cout << "Coarse rotate" << std::endl;
     if ( debug_ ) printVals();
 
     if ( debug_ ) std::cout << "Starting iterations" << std::endl;
     for ( int i=1; i<=iterations_; ++i )
     {
         int sign = (y>=0) ? -1:1;
         int xtmp = x - sign*(y>>i);
         int ytmp = y + sign*(x>>i);
         x = xtmp;
         y = ytmp;
         rotation += sign*rotations_[i-1];
         if ( debug_ ) printVals();
     }
     
     // need a little extra room for the last multiplication
     aMagnitude = ((long) x * (long) scaleFactor_)>>(2*internalBits_-outputBits_-1);
 
     // Xilinx seems to just mod to [-pi,pi]
     if ( rotation > encodedAngles_[Pi] ) rotation -= 2*encodedAngles_[Pi]+1;
     aPhi = (-rotation)>>(internalBits_-outputBits_);
 }