mirror of
https://github.com/simdjson/simdjson
synced 2026-06-08 17:27:07 +00:00
Daniel Lemire
66 lines
2.6 KiB
C++
66 lines
2.6 KiB
C++
namespace simdjson {
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namespace SIMDJSON_IMPLEMENTATION {
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namespace {
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/// @private
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namespace atomparsing {
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// The string_to_uint32 is exclusively used to map literal strings to 32-bit values.
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// We use memcpy instead of a pointer cast to avoid undefined behaviors since we cannot
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// be certain that the character pointer will be properly aligned.
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// You might think that using memcpy makes this function expensive, but you'd be wrong.
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// All decent optimizing compilers (GCC, clang, Visual Studio) will compile string_to_uint32("false");
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// to the compile-time constant 1936482662.
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simdjson_really_inline uint32_t string_to_uint32(const char* str) { uint32_t val; std::memcpy(&val, str, sizeof(uint32_t)); return val; }
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// Again in str4ncmp we use a memcpy to avoid undefined behavior. The memcpy may appear expensive.
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// Yet all decent optimizing compilers will compile memcpy to a single instruction, just about.
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simdjson_warn_unused
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simdjson_really_inline uint32_t str4ncmp(const uint8_t *src, const char* atom) {
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uint32_t srcval; // we want to avoid unaligned 32-bit loads (undefined in C/C++)
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static_assert(sizeof(uint32_t) <= SIMDJSON_PADDING, "SIMDJSON_PADDING must be larger than 4 bytes");
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std::memcpy(&srcval, src, sizeof(uint32_t));
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return srcval ^ string_to_uint32(atom);
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}
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simdjson_warn_unused
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simdjson_really_inline bool is_valid_true_atom(const uint8_t *src) {
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return (str4ncmp(src, "true") | jsoncharutils::is_not_structural_or_whitespace(src[4])) == 0;
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}
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simdjson_warn_unused
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simdjson_really_inline bool is_valid_true_atom(const uint8_t *src, size_t len) {
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if (len > 4) { return is_valid_true_atom(src); }
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else if (len == 4) { return !str4ncmp(src, "true"); }
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else { return false; }
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}
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simdjson_warn_unused
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simdjson_really_inline bool is_valid_false_atom(const uint8_t *src) {
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return (str4ncmp(src+1, "alse") | jsoncharutils::is_not_structural_or_whitespace(src[5])) == 0;
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}
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simdjson_warn_unused
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simdjson_really_inline bool is_valid_false_atom(const uint8_t *src, size_t len) {
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if (len > 5) { return is_valid_false_atom(src); }
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else if (len == 5) { return !str4ncmp(src+1, "alse"); }
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else { return false; }
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}
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simdjson_warn_unused
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simdjson_really_inline bool is_valid_null_atom(const uint8_t *src) {
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return (str4ncmp(src, "null") | jsoncharutils::is_not_structural_or_whitespace(src[4])) == 0;
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}
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simdjson_warn_unused
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simdjson_really_inline bool is_valid_null_atom(const uint8_t *src, size_t len) {
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if (len > 4) { return is_valid_null_atom(src); }
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else if (len == 4) { return !str4ncmp(src, "null"); }
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else { return false; }
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}
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} // namespace atomparsing
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} // unnamed namespace
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} // namespace SIMDJSON_IMPLEMENTATION
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} // namespace simdjson
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