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253 lines
6.5 KiB
C++
253 lines
6.5 KiB
C++
//
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// Blitter.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 22/07/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#include "Blitter.hpp"
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#include "Minterms.h"
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//#define NDEBUG
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#define LOG_PREFIX "[Blitter] "
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#include "../../Outputs/Log.hpp"
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using namespace Amiga;
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void Blitter::set_control(int index, uint16_t value) {
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if(index) {
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line_mode_ = (value & 0x0001);
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one_dot_ = value & 0x0002;
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line_direction_ = (value >> 2) & 7;
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line_sign_ = (value & 0x0040) ? -1 : 1;
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direction_ = one_dot_ ? uint32_t(-1) : uint32_t(1);
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inclusive_fill_ = (value & 0x0008);
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exclusive_fill_ = (value & 0x0010);
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fill_carry_ = (value & 0x0004);
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} else {
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minterms_ = value & 0xff;
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channel_enables_[3] = value & 0x100;
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channel_enables_[2] = value & 0x200;
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channel_enables_[1] = value & 0x400;
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channel_enables_[0] = value & 0x800;
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}
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shifts_[index] = value >> 12;
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LOG("Set control " << index << " to " << PADHEX(4) << value);
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}
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void Blitter::set_first_word_mask(uint16_t value) {
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LOG("Set first word mask: " << PADHEX(4) << value);
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a_mask_[0] = value;
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}
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void Blitter::set_last_word_mask(uint16_t value) {
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LOG("Set last word mask: " << PADHEX(4) << value);
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a_mask_[1] = value;
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}
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void Blitter::set_size(uint16_t value) {
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width_ = (width_ & ~0x3f) | (value & 0x3f);
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height_ = (height_ & ~0x3ff) | (value >> 6);
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LOG("Set size to " << std::dec << width_ << ", " << height_);
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// Current assumption: writing this register informs the
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// blitter that it should treat itself as about to start a new line.
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}
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void Blitter::set_minterms(uint16_t value) {
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LOG("Set minterms " << PADHEX(4) << value);
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minterms_ = value & 0xff;
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}
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void Blitter::set_vertical_size(uint16_t value) {
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LOG("Set vertical size " << PADHEX(4) << value);
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}
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void Blitter::set_horizontal_size(uint16_t value) {
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LOG("Set horizontal size " << PADHEX(4) << value);
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}
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void Blitter::set_modulo(int channel, uint16_t value) {
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LOG("Set modulo size " << channel << " to " << PADHEX(4) << value);
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// Convert by sign extension.
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modulos_[channel] = uint32_t(int16_t(value) >> 1);
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}
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void Blitter::set_data(int channel, uint16_t value) {
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LOG("Set data " << channel << " to " << PADHEX(4) << value);
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// Ugh, backed myself into a corner. TODO: clean.
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switch(channel) {
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case 0: a_ = value; break;
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case 1: b_ = value; break;
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case 2: c_ = value; break;
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default: break;
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}
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}
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uint16_t Blitter::get_status() {
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LOG("Returned status of " << (height_ ? 0x8000 : 0x0000));
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return height_ ? 0x8000 : 0x0000;
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}
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bool Blitter::advance() {
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if(!height_) return false;
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if(line_mode_) {
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//
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// Line mode.
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//
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// Bluffer's guide to line mode:
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//
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// In Bresenham terms, the following registers have been set up:
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//
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// [A modulo] = 4 * (dy - dx)
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// [B modulo] = 4 * dy
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// [A pointer] = 4 * dy - 2 * dx, with the sign flag in BLTCON1 indicating sign.
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//
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// [A data] = 0x8000
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// [Both masks] = 0xffff
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// [A shift] = x1 & 15
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//
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// [B data] = texture
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// [B shift] = bit at which to start the line texture (0 = LSB)
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//
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// [C and D pointers] = word containing the first pixel of the line
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// [C and D modulo] = width of the bitplane in bytes
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//
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// height = number of pixels
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//
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// If ONEDOT of BLTCON1 is set, plot only a single bit per horizontal row.
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//
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// BLTCON1 quadrants are (bits 2–4):
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//
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// 110 -> step in x, x positive, y negative
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// 111 -> step in x, x negative, y negative
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// 101 -> step in x, x negative, y positive
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// 100 -> step in x, x positive, y positive
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//
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// 001 -> step in y, x positive, y negative
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// 011 -> step in y, x negative, y negative
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// 010 -> step in y, x negative, y positive
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// 000 -> step in y, x positive, y positive
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//
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// So that's:
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//
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// * bit 4 = x [=1] or y [=0] major;
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// * bit 3 = 1 => major variable negative; otherwise positive;
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// * bit 2 = 1 => minor variable negative; otherwise positive.
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//
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// Implementation below is heavily based on the documentation found
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// at https://github.com/niklasekstrom/blitter-subpixel-line/blob/master/Drawing%20lines%20using%20the%20Amiga%20blitter.pdf
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//
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int error = int16_t(pointer_[0] << 1) >> 1; // TODO: what happens if line_sign_ doesn't agree with this?
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bool draw_ = true;
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while(height_--) {
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if(draw_) {
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// TODO: patterned lines. Unclear what to do with the bit that comes out of b.
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// Probably extend it to a full word?
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c_ = ram_[pointer_[3] & ram_mask_];
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ram_[pointer_[3] & ram_mask_] =
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apply_minterm<uint16_t>(a_ >> shifts_[0], b_, c_, minterms_);
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draw_ &= !one_dot_;
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}
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constexpr int LEFT = 1 << 0;
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constexpr int RIGHT = 1 << 1;
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constexpr int UP = 1 << 2;
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constexpr int DOWN = 1 << 3;
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int step = (line_direction_ & 4) ?
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((line_direction_ & 1) ? LEFT : RIGHT) :
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((line_direction_ & 1) ? UP : DOWN);
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if(error < 0) {
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error += modulos_[1];
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} else {
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step |=
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(line_direction_ & 4) ?
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((line_direction_ & 2) ? UP : DOWN) :
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((line_direction_ & 2) ? LEFT : RIGHT);
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error += modulos_[0];
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}
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if(step & LEFT) {
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--shifts_[0];
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if(shifts_[0] == -1) {
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--pointer_[3];
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}
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} else if(step & RIGHT) {
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++shifts_[0];
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if(shifts_[0] == 16) {
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++pointer_[3];
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}
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}
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shifts_[0] &= 15;
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if(step & UP) {
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pointer_[3] -= modulos_[2];
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draw_ = true;
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} else if(step & DOWN) {
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pointer_[3] += modulos_[2];
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draw_ = true;
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}
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}
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} else {
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// Copy mode.
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// Quick hack: do the entire action atomically.
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for(int y = 0; y < height_; y++) {
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for(int x = 0; x < width_; x++) {
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if(channel_enables_[0]) {
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a32_ = (a32_ << 16) | ram_[pointer_[0] & ram_mask_];
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a_ = uint16_t(a32_ >> shifts_[0]);
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pointer_[0] += direction_;
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}
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if(channel_enables_[1]) {
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b32_ = (b32_ << 16) | ram_[pointer_[1] & ram_mask_];
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b_ = uint16_t(b32_ >> shifts_[1]);
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pointer_[1] += direction_;
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}
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if(channel_enables_[2]) {
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c_ = ram_[pointer_[2] & ram_mask_];
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pointer_[2] += direction_;
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}
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if(channel_enables_[3]) {
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uint16_t a_mask = 0xffff;
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if(x == 0) a_mask &= a_mask_[0];
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if(x == width_ - 1) a_mask &= a_mask_[1];
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ram_[pointer_[3] & ram_mask_] =
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apply_minterm<uint16_t>(
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a_ & a_mask, // TODO: is this properly-placed?
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b_,
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c_,
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minterms_);
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pointer_[3] += direction_;
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}
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}
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pointer_[0] += modulos_[0] * channel_enables_[0];
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pointer_[1] += modulos_[1] * channel_enables_[1];
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pointer_[2] += modulos_[2] * channel_enables_[2];
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pointer_[3] += modulos_[3] * channel_enables_[3];
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}
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}
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height_ = 0;
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return true;
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}
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