| # Copyright (C) 2020 Arm Limited or its affiliates. All rights reserved. |
| # |
| # Copyright 2015 The Gemmlowp Authors. All Rights Reserved. |
| # |
| # SPDX-License-Identifier: Apache-2.0 |
| # |
| # Licensed under the Apache License, Version 2.0 (the "License"); |
| # you may not use this file except in compliance with the License. |
| # You may obtain a copy of the License at |
| # |
| # http://www.apache.org/licenses/LICENSE-2.0 |
| # |
| # Unless required by applicable law or agreed to in writing, software |
| # distributed under the License is distributed on an "AS IS" BASIS, |
| # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| # See the License for the specific language governing permissions and |
| # limitations under the License. |
| # |
| # Description: |
| # Contains various fixed point math functions based on the gemmlowp fixed |
| # point implementation. |
| import numpy as np |
| |
| |
| def saturating_rounding_mul(a, b): |
| assert np.int32(a) == a |
| assert np.int32(b) == b |
| if a == b and a == np.iinfo(np.int32).min: |
| return np.int32(np.iinfo(np.int32).max) |
| ab = np.int64(a) * np.int64(b) |
| nudge = (1 << 30) if ab >= 0 else (1 - (1 << 30)) |
| result = np.int32(np.right_shift(ab + nudge, 31)) |
| if result < 0: |
| result += 1 |
| return result |
| |
| |
| def shift_left(a, offset): |
| assert np.int32(a) == a |
| assert offset >= 0 |
| a_info = np.iinfo(a) |
| shifted = a * (1 << offset) |
| if shifted < a_info.min: |
| return np.int32(a_info.min) |
| elif shifted > a_info.max: |
| return np.int32(a_info.max) |
| else: |
| return np.int32(shifted) |
| |
| |
| def rounding_divide_by_pot(x, exponent): |
| assert np.int32(x) == x |
| assert np.int32(exponent) == exponent |
| mask = (1 << exponent) - 1 |
| remainder = x & mask |
| threshold = mask >> 1 |
| if x < 0: |
| threshold += 1 |
| result = x >> exponent |
| if remainder > threshold: |
| result += 1 |
| return result |
| |
| |
| def saturating_rounding_multiply_by_pot(exponent, x): |
| assert np.int32(x) == x |
| assert np.int32(exponent) == exponent |
| threshold = (1 << (np.iinfo(np.int32).bits - 1 - exponent)) - 1 |
| if x > threshold: |
| return np.iinfo(np.int32).max |
| elif x < -threshold: |
| return np.iinfo(np.int32).min |
| else: |
| return shift_left(x, exponent) |
| |
| |
| def rescale(integer_bits_src, integer_bits_dst, x): |
| assert np.int32(integer_bits_src) == integer_bits_src |
| assert np.int32(integer_bits_dst) == integer_bits_dst |
| assert np.int32(x) == x |
| exponent = integer_bits_src - integer_bits_dst |
| result = saturating_rounding_multiply_by_pot(exponent, x) |
| return result |
| |
| |
| # Input Q0.31 |
| def exp_on_interval_between_negative_one_quarter_and_0_excl(a): |
| assert np.int32(a) == a |
| assert -1 << (31 - 2) <= a < 0 |
| offset = 28 |
| constant_term = 1895147668 |
| constant_1_over_3 = 715827883 |
| x = a + (1 << offset) |
| x2 = saturating_rounding_mul(x, x) |
| x3 = saturating_rounding_mul(x2, x) |
| x4 = saturating_rounding_mul(x2, x2) |
| x4_over_4 = rounding_divide_by_pot(x4, 2) |
| x4_over_24_plus_x3_over_6_plus_x2_over_2 = rounding_divide_by_pot( |
| saturating_rounding_mul((x4_over_4 + x3), constant_1_over_3) + x2, 1 |
| ) |
| |
| return np.int32( |
| constant_term + saturating_rounding_mul(constant_term, x + x4_over_24_plus_x3_over_6_plus_x2_over_2) |
| ) |
| |
| |
| # Input Q5.26 |
| def exp_on_negative_values(a): |
| assert np.int32(a) == a |
| assert a <= 0 |
| one_quarter = np.int32(16777216) |
| mask = np.int32(16777215) |
| a_mod_quarter_minus_one_quarter = np.int32((a & mask) - one_quarter) |
| |
| result = exp_on_interval_between_negative_one_quarter_and_0_excl(rescale(5, 0, a_mod_quarter_minus_one_quarter)) |
| remainder = np.int32(a_mod_quarter_minus_one_quarter - a) |
| |
| def exp_barrel_shifter(exponent, multiplier, result): |
| fractional_bits = 26 |
| integer_bits = 5 |
| shift = fractional_bits + exponent if integer_bits > exponent else 0 |
| if remainder & (1 << shift): |
| return saturating_rounding_mul(result, multiplier) |
| else: |
| return result |
| |
| result = exp_barrel_shifter(-2, 1672461947, result) |
| result = exp_barrel_shifter(-1, 1302514674, result) |
| result = exp_barrel_shifter(+0, 790015084, result) |
| result = exp_barrel_shifter(+1, 290630308, result) |
| result = exp_barrel_shifter(+2, 39332535, result) |
| result = exp_barrel_shifter(+3, 720401, result) |
| result = exp_barrel_shifter(+4, 242, result) |
| |
| if a == 0: |
| return np.iinfo(np.int32).max |
| else: |
| return result |