mirror of
https://gitlab.com/80486DX2-66/gists
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99 lines
2.1 KiB
C
99 lines
2.1 KiB
C
/*
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* fwrite_le.c
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*
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* Author: Intel A80486DX2-66
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* License: Creative Commons Zero 1.0 Universal
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*/
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#include "fwrite_le.h"
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int detect_endianness(void) {
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volatile uint32_t i = 0x01234567;
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uint8_t* bytes = (uint8_t*)(&i);
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if (bytes[0] == 0x01 &&
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bytes[1] == 0x23 &&
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bytes[2] == 0x45 &&
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bytes[3] == 0x67)
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return DETECTED_BIG_ENDIAN;
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else if (
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bytes[0] == 0x67 &&
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bytes[1] == 0x45 &&
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bytes[2] == 0x23 &&
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bytes[3] == 0x01)
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return DETECTED_LITTLE_ENDIAN;
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return UNSUPPORTED_ENDIANNESS;
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}
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void reorder_le_be(
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#if FWRITE_LE_NO_MODIFICATION
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uint8_t* dest, uint8_t* src,
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#else
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uint8_t* bytes,
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#endif
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size_t count, size_t step) {
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for (size_t i = 0; i < count; i += step) {
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const size_t div_size = step / 2;
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for (size_t j = 0; j < div_size; j++) {
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const size_t old_pos = i + j, new_pos = i + step - j - 1;
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#if FWRITE_LE_NO_MODIFICATION
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dest[old_pos] = src[new_pos];
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dest[new_pos] = src[old_pos];
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#else
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uint8_t temp = bytes[old_pos];
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bytes[old_pos] = bytes[new_pos];
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bytes[new_pos] = temp;
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#endif
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}
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}
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}
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size_t fwrite_le(void* ptr, size_t size, size_t count, FILE* stream) {
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/*
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* warning: this function modifies `void* ptr` by default!
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* (if FWRITE_LE_NO_MODIFICATION in the header is 0)
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*/
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if (ptr == NULL)
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return 0;
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int endianness = detect_endianness();
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if (endianness == UNSUPPORTED_ENDIANNESS) {
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fprintf(stderr, "Unsupported endianness\n");
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exit(EXIT_FAILURE);
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} else if (endianness == DETECTED_LITTLE_ENDIAN)
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return fwrite(ptr, size, count, stream);
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// case: big-endian
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size_t bytes_count = size * count;
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#if FWRITE_LE_NO_MODIFICATION
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uint8_t* bytes = calloc(bytes_count, sizeof(uint8_t));
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if (bytes == NULL) {
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perror("calloc");
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exit(EXIT_FAILURE);
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}
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memcpy(bytes, ptr, bytes_count);
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#endif
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reorder_le_be(
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#if FWRITE_LE_NO_MODIFICATION
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bytes,
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#endif
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(uint8_t*) ptr, bytes_count, size);
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#if FWRITE_LE_NO_MODIFICATION
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size_t res =
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#else
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return
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#endif
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fwrite(
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#if FWRITE_LE_NO_MODIFICATION
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bytes,
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#else
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(uint8_t*) ptr,
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#endif
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size, count, stream);
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#if FWRITE_LE_NO_MODIFICATION
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free(bytes);
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return res;
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#endif
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}
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