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# Copyright © 2020 Arm Ltd. All rights reserved.
# SPDX-License-Identifier: MIT
"""
This file contains functions relating to quantizing and dequantizing values.
"""
from .._generated.pyarmnn import Quantize_uint8_t, Quantize_int8_t, Quantize_int16_t, Quantize_int32_t, \
Dequantize_uint8_t, Dequantize_int8_t, Dequantize_int16_t, Dequantize_int32_t
__DTYPE_TO_QUANTIZE_FUNCTION = {
'uint8': Quantize_uint8_t,
'int8': Quantize_int8_t,
'int16': Quantize_int16_t,
'int32': Quantize_int32_t
}
__DTYPE_TO_DEQUANTIZE_FUNCTION = {
'uint8': ((0, 255), Dequantize_uint8_t),
'int8': ((-128, 127), Dequantize_int8_t),
'int16': ((-32768, 32767), Dequantize_int16_t),
'int32': ((-2147483648, 2147483647), Dequantize_int32_t)
}
def quantize(value: float, scale: float, offset: int, target_dtype: str) -> int:
"""Quantize the given value to the given target datatype using Arm NN.
This function can be used to convert a 32-bit floating point value into 8/16/32-bit signed
integer or 8-bit unsigned integer values.
Args:
value (float): The value to be quantized.
scale (float): A numeric constant that the value is multiplied by.
offset (int): A 'zero-point' used to 'shift' the integer range.
target_dtype (str): The target data type. Supported values: 'unit8', 'int8', 'int16', 'int32'.
Returns:
int: A quantized 8-bit unsigned integer value or 8/16/32-bit signed integer value.
"""
if target_dtype not in __DTYPE_TO_QUANTIZE_FUNCTION:
raise ValueError("""Unexpected target datatype {} given.
Armnn currently supports quantization to {} values.""".format(target_dtype, list(__DTYPE_TO_QUANTIZE_FUNCTION.keys())))
return __DTYPE_TO_QUANTIZE_FUNCTION[target_dtype](float(value), scale, offset)
def dequantize(value: int, scale: float, offset: float, from_dtype: str) -> float:
"""Dequantize the given value from the given datatype using Arm NN.
This function can be used to convert an 8-bit unsigned integer value or 8/16/32-bit signed
integer value into a 32-bit floating point value. Typically used when decoding an
output value from an output tensor on a quantized model.
Args:
value (int): The value to be dequantized. Value could be numpy numeric data type.
scale (float): A numeric constant that the value is multiplied by.
offset (float): A 'zero-point' used to 'shift' the integer range.
from_dtype (str): The data type 'value' represents. Supported values: 'unit8', 'int8', 'int16', 'int32'.
Returns:
float: A dequantized 32-bit floating-point value.
"""
# specifies which function to use with given datatype and the value range for that data type.
if from_dtype not in __DTYPE_TO_DEQUANTIZE_FUNCTION:
raise ValueError("""Unexpected value datatype {} given.
Armnn currently supports dequantization from {} values.""".format(from_dtype, list(__DTYPE_TO_DEQUANTIZE_FUNCTION.keys())))
input_range = __DTYPE_TO_DEQUANTIZE_FUNCTION[from_dtype][0]
if not input_range[0] <= value <= input_range[1]:
raise ValueError('Value is not within range of the given datatype {}'.format(from_dtype))
return __DTYPE_TO_DEQUANTIZE_FUNCTION[from_dtype][1](int(value), scale, offset)
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