24 lines
639 B
Plaintext
24 lines
639 B
Plaintext
// polynomial for approximating atan(x) and atan2(y, x)
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//
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// Copyright (c) 2022-2023, Arm Limited.
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// SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
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// atan is odd, so approximate with an odd polynomial:
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// x + ax^3 + bx^5 + cx^7 + ...
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// We generate a, b, c, ... such that we can approximate atan(x) by:
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// x + x^3 * (a + bx^2 + cx^4 + ...)
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// Assemble monomials
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deg = 20;
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mons = [|1,...,deg|];
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for i from 0 to deg-1 do mons[i] = mons[i] * 2 + 1;
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a = 0x1.0p-1022;
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b = 1;
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poly = fpminimax(atan(x)-x, mons, [|double ...|], [a;b]);
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display = hexadecimal;
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print("coeffs:");
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for i from 0 to deg-1 do coeff(poly,mons[i]);
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