154 lines
3.3 KiB
C
154 lines
3.3 KiB
C
#include <windows.h>
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#include <assert.h>
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#include <stdbool.h>
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#include <stddef.h>
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#include <stdint.h>
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#include "hook/iobuf.h"
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#include "jvs/jvs-frame.h"
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#include "util/dprintf.h"
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static HRESULT jvs_frame_check_sum(const struct iobuf *dest);
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static HRESULT jvs_frame_encode_byte(struct iobuf *dest, uint8_t byte);
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/* Deals in whole frames only for simplicity's sake, since that's all we need
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to emulate the Nu's kernel driver interface. This could of course be
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extended later for other arcade hardware platforms. */
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HRESULT jvs_frame_decode(
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struct iobuf *dest,
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const void *ptr,
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size_t nbytes)
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{
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const uint8_t *bytes;
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bool escape;
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size_t i;
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assert(dest != NULL);
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assert(ptr != NULL);
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bytes = ptr;
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if (nbytes == 0) {
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dprintf("JVS Frame: Empty frame\n");
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return E_FAIL;
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}
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if (bytes[0] != 0xE0) {
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dprintf("JVS Frame: Sync byte was expected\n");
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return E_FAIL;
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}
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escape = false;
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for (i = 1 ; i < nbytes ; i++) {
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if (bytes[i] == 0xE0) {
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dprintf("JVS Frame: Unexpected sync byte\n");
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return E_FAIL;
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} else if (bytes[i] == 0xD0) {
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if (escape) {
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dprintf("JVS Frame: Escaping fault\n");
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return E_FAIL;
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}
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escape = true;
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} else {
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if (dest->pos >= dest->nbytes) {
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dprintf("JVS Frame: Insufficiant Buffer\n");
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return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
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}
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if (escape) {
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escape = false;
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dest->bytes[dest->pos++] = bytes[i] + 1;
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} else {
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dest->bytes[dest->pos++] = bytes[i];
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}
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}
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}
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return jvs_frame_check_sum(dest);
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}
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static HRESULT jvs_frame_check_sum(const struct iobuf *dest)
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{
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uint8_t checksum;
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size_t i;
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checksum = 0;
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for (i = 0 ; i < dest->pos - 1 ; i++) {
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checksum += dest->bytes[i];
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}
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if (checksum != dest->bytes[dest->pos - 1]) {
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dprintf("JVS Frame: Checksum failure\n");
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return HRESULT_FROM_WIN32(ERROR_CRC);
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}
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return S_OK;
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}
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HRESULT jvs_frame_encode(
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struct iobuf *dest,
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const void *ptr,
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size_t nbytes)
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{
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const uint8_t *bytes;
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uint8_t checksum;
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size_t i;
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HRESULT hr;
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assert(dest != NULL);
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assert(ptr != NULL);
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bytes = ptr;
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checksum = 0;
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if (dest->pos + 1 > dest->nbytes) {
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return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
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}
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dest->bytes[dest->pos++] = 0xE0;
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for (i = 0 ; i < nbytes ; i++) {
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hr = jvs_frame_encode_byte(dest, bytes[i]);
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if (FAILED(hr)) {
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return hr;
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}
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checksum += bytes[i];
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}
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return jvs_frame_encode_byte(dest, checksum);
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}
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static HRESULT jvs_frame_encode_byte(struct iobuf *dest, uint8_t byte)
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{
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if (byte == 0xD0 || byte == 0xE0) {
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if (dest->pos + 2 > dest->nbytes) {
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return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
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}
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dest->bytes[dest->pos++] = 0xD0;
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dest->bytes[dest->pos++] = byte - 1;
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} else {
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if (dest->pos + 1 > dest->nbytes) {
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return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
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}
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dest->bytes[dest->pos++] = byte;
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}
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return S_OK;
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}
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