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Add readahead to VariantParser

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Adds a readahead buffer to VariantParser, to prevent large numbers of freads for single bytes, which is inefficient.
This commit is contained in:
lawnjelly
2022-08-30 11:42:36 +01:00
parent 073032b6d0
commit 29d4d4105e
2 changed files with 84 additions and 28 deletions
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77
core/variant_parser.cpp
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@@ -35,36 +35,77 @@
#include "core/os/keyboard.h"
#include "core/string_buffer.h"
CharType VariantParser::StreamFile::get_char() {
return f->get_8();
CharType VariantParser::Stream::get_char() {
// is within buffer?
if (readahead_pointer < readahead_filled) {
return readahead_buffer[readahead_pointer++];
}
// attempt to readahead
readahead_filled = _read_buffer(readahead_buffer, READAHEAD_SIZE);
if (readahead_filled) {
readahead_pointer = 0;
} else {
// EOF
readahead_pointer = 1;
eof = true;
return 0;
}
return get_char();
}
uint32_t VariantParser::StreamFile::_read_buffer(CharType *p_buffer, uint32_t p_num_chars) {
// The buffer is assumed to include at least one character (for null terminator)
ERR_FAIL_COND_V(!p_num_chars, 0);
uint8_t *temp = (uint8_t *)alloca(p_num_chars);
uint64_t num_read = f->get_buffer(temp, p_num_chars);
ERR_FAIL_COND_V(num_read == UINT64_MAX, 0);
// translate to wchar
for (uint32_t n = 0; n < num_read; n++) {
p_buffer[n] = temp[n];
}
// could be less than p_num_chars, or zero
return num_read;
}
bool VariantParser::StreamFile::is_utf8() const {
return true;
}
bool VariantParser::StreamFile::is_eof() const {
return f->eof_reached();
}
CharType VariantParser::StreamString::get_char() {
if (pos > s.length()) {
return 0;
} else if (pos == s.length()) {
// You need to try to read again when you have reached the end for EOF to be reported,
// so this works the same as files (like StreamFile does)
pos++;
return 0;
} else {
return s[pos++];
uint32_t VariantParser::StreamString::_read_buffer(CharType *p_buffer, uint32_t p_num_chars) {
// The buffer is assumed to include at least one character (for null terminator)
ERR_FAIL_COND_V(!p_num_chars, 0);
int available = MAX(s.length() - pos, 0);
if (available >= (int)p_num_chars) {
const CharType *src = s.ptr();
src += pos;
memcpy(p_buffer, src, p_num_chars * sizeof(CharType));
pos += p_num_chars;
return p_num_chars;
}
// going to reach EOF
if (available) {
const CharType *src = s.ptr();
src += pos;
memcpy(p_buffer, src, available * sizeof(CharType));
pos += available;
}
// add a zero
p_buffer[available] = 0;
return available;
}
bool VariantParser::StreamString::is_utf8() const {
return false;
}
bool VariantParser::StreamString::is_eof() const {
return pos > s.length();
}
/////////////////////////////////////////////////////////////////////////////////////////////////