Public Access
25 lines
958 B
C
25 lines
958 B
C
 
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#pragma once
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#include <stdint.h>
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// CRC-16/CCITT-FALSE of a display buffer as BROSE9323 keeps it: rows of (width + 7) / 8
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// bytes, bit (x & 7) is dot x. The unused bits at the end of each row are left out, so
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// only the dots count (fillScreen sets them, drawPixel never does). The Nano answers the
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// C command with it; the ESP32 compares it with its own copy (src/esp32/nano_link).
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inline uint16_t bufferCrc(const uint8_t *buffer, uint8_t width, uint8_t height)
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{
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const uint8_t row_bytes = (width + 7) / 8;
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const uint8_t last_mask = (width & 7) ? (uint8_t)((1 << (width & 7)) - 1) : 0xFF;
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uint16_t crc = 0xFFFF;
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for (uint8_t y = 0; y < height; y++)
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for (uint8_t i = 0; i < row_bytes; i++)
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{
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uint8_t b = buffer[y * row_bytes + i];
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if (i == row_bytes - 1)
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b &= last_mask;
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crc ^= (uint16_t)b << 8;
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for (uint8_t k = 0; k < 8; k++)
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crc = (crc & 0x8000) ? (uint16_t)((crc << 1) ^ 0x1021) : (uint16_t)(crc << 1);
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}
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return crc;
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}
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