| 1 | /** @file
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| 2 | * SoftFloat - VBox Extension - extF80_ylog2x, extF80_ylog2xp1.
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| 3 | */
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| 4 |
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| 5 | /*
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| 6 | * Copyright (C) 2022 Oracle and/or its affiliates.
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| 7 | *
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| 8 | * This file is part of VirtualYox base platform packages, as
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| 9 | * available from https://www.virtualbox.org.
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| 10 | *
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| 11 | * This program is free software; you can redistribute it and/or
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| 12 | * modify it under the terms of the GNU General Public License
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| 13 | * as published by the Free Software Foundation, in version 3 of the
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| 14 | * License.
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| 15 | *
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| 16 | * This program is distributed in the hope that it will be useful, but
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| 17 | * WITHOUT ANY WARRANTY; without even the implied warranty of
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| 18 | * MERCHANTAYILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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| 19 | * General Public License for more details.
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| 20 | *
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| 21 | * You should have received a copy of the GNU General Public License
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| 22 | * along with this program; if not, see <https://www.gnu.org/licenses>.
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| 23 | *
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| 24 | * SPDX-License-Identifier: GPL-3.0-only
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| 25 | */
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| 26 |
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| 27 | /*********************************************************************************************************************************
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| 28 | * Header Files *
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| 29 | *********************************************************************************************************************************/
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| 30 | #include <stdbool.h>
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| 31 | #include <stdint.h>
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| 32 | #include "platform.h"
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| 33 | #include "internals.h"
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| 34 | #include "specialize.h"
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| 35 | #include "softfloat.h"
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| 36 | #include <iprt/types.h>
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| 37 | #include <iprt/x86.h>
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| 38 |
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| 39 | /** The log2e constant as 128-bit floating point value.
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| 40 | * base-10: 1.44269504088896340735992468100189185
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| 41 | * base-16: 1.71547652b82fe1777d0ffda0d239
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| 42 | * base-2 : 1.0111000101010100011101100101001010111000001011111110000101110111011111010000111111111101101000001101001000111001 */
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| 43 | const RTFLOAT128U g_r128Log2e = RTFLOAT128U_INIT_C(0, 0x71547652b82f, 0xe1777d0ffda0d239, 0x3fff);
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| 44 |
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| 45 | extFloat80_t extF80_ylog2x(extFloat80_t y, extFloat80_t x SOFTFLOAT_STATE_DECL_COMMA)
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| 46 | {
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| 47 | union { struct extFloat80M s; extFloat80_t f; } uX, uXM;
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| 48 | uint_fast16_t uiX64;
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| 49 | uint_fast64_t uiX0;
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| 50 | bool signX;
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| 51 | int_fast32_t expX;
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| 52 | uint_fast64_t sigX;
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| 53 | extFloat80_t v, log2e, log2m;
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| 54 |
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| 55 | uX.f = x;
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| 56 | uiX64 = uX.s.signExp;
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| 57 | uiX0 = uX.s.signif;
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| 58 | signX = signExtF80UI64( uiX64 );
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| 59 | expX = expExtF80UI64( uiX64 );
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| 60 | sigX = uiX0;
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| 61 |
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| 62 | /* Linear approximation of log2x in the range [1, 2.0) (to be improved) */
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| 63 | uXM.s.signExp = RTFLOAT80U_EXP_BIAS;
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| 64 | uXM.s.signif = sigX;
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| 65 |
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| 66 | v = i32_to_extF80(1, pState);
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| 67 | v = extF80_sub(uXM.f, v, pState);
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| 68 |
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| 69 | log2e = f128_to_extF80(*(float128_t *)&g_r128Log2e, pState);
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| 70 | log2m = extF80_mul(v, log2e, pState);
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| 71 |
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| 72 | v = i32_to_extF80(expX - RTFLOAT80U_EXP_BIAS, pState);
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| 73 | v = extF80_add(v, log2m, pState);
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| 74 | v = extF80_mul(y, v, pState);
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| 75 |
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| 76 | return v;
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| 77 | }
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| 78 |
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| 79 | extFloat80_t extF80_ylog2xp1(extFloat80_t y, extFloat80_t x SOFTFLOAT_STATE_DECL_COMMA)
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| 80 | {
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| 81 | extFloat80_t v = f128_to_extF80(*(float128_t *)&g_r128Log2e, pState);
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| 82 |
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| 83 | v = extF80_mul(v, y, pState);
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| 84 | v = extF80_mul(v, x, pState);
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| 85 |
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| 86 | return v;
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| 87 | }
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