mirror of https://github.com/fadden/6502bench.git
81 lines
3.3 KiB
C#
81 lines
3.3 KiB
C#
/*
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* Copyright 2018 faddenSoft
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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using System;
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using System.Diagnostics;
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namespace Asm65 {
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/// <summary>
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/// Small utility functions.
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/// </summary>
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public static class Helper {
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/// <summary>
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/// Computes the target address of an 8-bit relative branch instruction.
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/// </summary>
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/// <param name="addr">24-bit address of branch instruction opcode.</param>
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/// <param name="branchOffset">Branch operand.</param>
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/// <returns>Target address.</returns>
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public static int RelOffset8(int addr, sbyte branchOffset) {
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// Branch is relative to the start of the following instruction, so add 2.
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// Branches wrap around the current bank (in both directions), and the target
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// is in the same bank as source addr.
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Debug.Assert(addr >= 0 && addr <= 0xffffff);
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int target = (addr + 2 + branchOffset) & 0xffff;
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target |= addr & 0x7fff0000;
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return target;
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}
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/// <summary>
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/// Computes the target address of a 16-bit relative branch instruction.
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/// </summary>
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/// <param name="addr">24-bit address of branch instruction opcode.</param>
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/// <param name="branchOffset">Branch operand.</param>
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/// <returns>Target address.</returns>
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public static int RelOffset16(int addr, short branchOffset) {
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// Branch is relative to the start of the following instruction, so add 3.
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// Branches wrap around the current bank (in both directions), and the target
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// is in the same bank as source addr.
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Debug.Assert(addr >= 0 && addr <= 0xffffff);
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int target = (addr + 3 + branchOffset) & 0xffff;
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target |= addr & 0x7fff0000;
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return target;
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}
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/// <summary>
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/// Determines whether a range of bytes is composed of a single value. If so, the
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/// value is returned.
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/// </summary>
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/// <param name="data">Bytes to examine.</param>
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/// <param name="offset">Start offset.</param>
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/// <param name="length">Number of bytes. Must be greater than zero.</param>
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/// <returns>The value found, or -1 if multiple values were found.</returns>
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public static int CheckRangeHoldsSingleValue(byte[] data, int offset, int length) {
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Debug.Assert(data != null);
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Debug.Assert(offset >= 0 && offset < data.Length);
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Debug.Assert(length >= 0 && offset + length <= data.Length);
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if (length < 0) {
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return -1;
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}
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byte testVal = data[offset++];
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while (--length > 0) {
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if (data[offset++] != testVal) {
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return -1;
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}
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}
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return testVal;
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}
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}
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}
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