73 lines
1.9 KiB
C
73 lines
1.9 KiB
C
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#include "parser_internal.h"
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typedef struct {
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const HParser *p;
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char endianness;
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} HParseEndianness;
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// helper
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static void switch_bit_order(HInputStream *input)
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{
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assert(input->bit_offset <= 8);
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if((input->bit_offset % 8) != 0) {
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// switching bit order in the middle of a byte
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// we leave bit_offset untouched. this means that something like
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// le(bits(5)),le(bits(3))
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// is equivalent to
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// le(bits(5),bits(3)) .
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// on the other hand,
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// le(bits(5)),be(bits(5))
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// will read the same 5 bits twice and discard the top 3.
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} else {
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// flip offset (0 <-> 8)
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input->bit_offset = 8 - input->bit_offset;
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}
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}
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static HParseResult *parse_endianness(void *env, HParseState *state)
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{
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HParseEndianness *e = env;
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HParseResult *res = NULL;
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char diff = state->input_stream.endianness ^ e->endianness;
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if(!diff) {
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// all the same, nothing to do
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res = h_do_parse(e->p, state);
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} else {
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if(diff & BIT_BIG_ENDIAN)
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switch_bit_order(&state->input_stream);
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state->input_stream.endianness ^= diff;
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res = h_do_parse(e->p, state);
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state->input_stream.endianness ^= diff;
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if(diff & BIT_BIG_ENDIAN)
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switch_bit_order(&state->input_stream);
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}
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return res;
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}
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static const HParserVtable endianness_vt = {
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.parse = parse_endianness,
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.isValidRegular = h_false,
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.isValidCF = h_false,
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.desugar = NULL,
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.compile_to_rvm = h_not_regular,
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};
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HParser* h_with_endianness(char endianness, const HParser *p)
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{
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return h_with_endianness__m(&system_allocator, endianness, p);
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}
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HParser* h_with_endianness__m(HAllocator *mm__, char endianness, const HParser *p)
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{
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HParseEndianness *env = h_new(HParseEndianness, 1);
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env->endianness = endianness;
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env->p = p;
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return h_new_parser(mm__, &endianness_vt, env);
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}
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