functions.py

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# Computer vision - Binary neural networks demo software by HyperbeeAI.   #
# Copyrights © 2023 Hyperbee.AI Inc. All rights reserved. [email protected] #
###########################################################################
import torch, sys
import torch.nn as nn
from torch.autograd import Function

###################################################
### Quantization Functions
###     backward passes are straight through

## Up-Down (ud) quantization for wide last layer ("bigdata"). Used in QAT
class Q_ud_wide(Function):
    @staticmethod
    def forward(_, x, xb, extrab):
        up_factor   = 2**(xb-extrab-1)
        down_factor = 2**(xb-1)
        return x.mul(up_factor).add(.5).floor().div(down_factor)

    @staticmethod
    def backward(_, x):
        return x, None, None

## Up-Down (ud) quantization. Used in QAT
class Q_ud(Function):
    @staticmethod
    def forward(_, x, xb):
        updown_factor = 2**(xb-1)
        return x.mul(updown_factor).add(.5).floor().div(updown_factor)

    @staticmethod
    def backward(_, x):
        return x, None

## Up-Down (ud) quantization for antipodal binary. Used in qat-ap
class Q_ud_ap(Function):
    @staticmethod
    def forward(_, x):
        x = torch.sign(x).div(2.0) # antipodal (-1,+1) weights @HW correspond to (-0.5,+0.5) in qat 
        mask  = (x == 0)
        return x - mask.type(torch.FloatTensor).to(x.device).div(2.0)
        
    @staticmethod
    def backward(_, x):
        return x

## Up (u) quantization. Used in Eval/hardware
class Q_u(Function):
    @staticmethod
    def forward(_, x, xb):
        up_factor = 2**(8-xb)
        return x.mul(up_factor).add(.5).floor()    ### Burak: maxim has a .add(0.5) at the beginning, I think that's wrong

    @staticmethod
    def backward(_, x):
        return x, None

## Down (d) quantization. Used in Eval/hardware
class Q_d(Function):
    @staticmethod
    def forward(_, x, xb):
        down_factor = 2**(xb-1)
        return x.div(down_factor).add(.5).floor()  ### Burak: maxim has a .add(0.5) at the beginning, I think that's wrong

    @staticmethod
    def backward(_, x):
        return x, None


###################################################
### Quantization module 
###     ("umbrella" for Functions)
class quantization(nn.Module):
    def __init__(self, xb = 8, mode='updown', wide=False):
        super().__init__()
        self.xb   = xb
        self.mode = mode
        self.wide = wide

    def forward(self, x):
        if(self.mode=='updown'):
            if(self.wide):
                return Q_ud_wide.apply(x, self.xb, 1) 
            else:
                return Q_ud.apply(x, self.xb)
        elif(self.mode=='down'):
            if(self.wide):
                return Q_d.apply(x, self.xb + 1) 
            else:
                return Q_d.apply(x, self.xb)
        elif(self.mode=='up'):
            return Q_u.apply(x, self.xb)
        elif(self.mode=='updown_ap'):
            return Q_ud_ap.apply(x)
        else:
        	print('wrong quantization mode. exiting')
        	sys.exit()

###################################################
### Clamping modules
### (doesn't need Functions since backward passes are well-defined)
class clamping_qa(nn.Module):
    def __init__(self, xb = 8, wide=False):
        super().__init__()
        if(wide):
            self.min_val = -16384.0  
            self.max_val =  16383.0  
        else:
            self.min_val = -1.0
            self.max_val = (2**(xb-1)-1)/(2**(xb-1))	    	

    def forward(self, x):
        return x.clamp(min=self.min_val, max=self.max_val)

class clamping_hw(nn.Module):
    def __init__(self, xb = 8, wide=False):
        super().__init__()
        if(wide):
            self.min_val = -2**(30-1)   
            self.max_val =  2**(30-1)-1 
        else:
            self.min_val = -2**(xb-1)
            self.max_val =  2**(xb-1)-1

    def forward(self, x):
        return x.clamp(min=self.min_val, max=self.max_val)


###################################################
### Computing output_shift, i.e., "los"
def calc_out_shift(weight, bias, shift_quantile):
    bias_r = torch.flatten(bias)
    weight_r = torch.flatten(weight)
    params_r = torch.cat((weight_r, bias_r))
    limit = torch.quantile(params_r.abs(), shift_quantile)
    return -(1./limit).log2().floor().clamp(min=-15., max=15.)