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84939c11bea3b51417a8c33a11acd4512b13cb48
json/tests/src/unit-class_lexer.cpp
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Niels LohmannandClaude Opus 4.8 84939c11be Add a contiguous fast path for scanning numbers 
scan_number() reads a number one character at a time through the input
adapter (get()) and appends each byte to token_buffer (add()) before
converting. For contiguous input, the per-character get()/add() overhead
dominates: it is roughly two thirds of the time spent on number-heavy
parsing, far more than the value conversion itself.

Add scan_number_bulk_contiguous(), which parses the whole number token
straight from the input buffer: it validates and classifies the extent
with the same grammar as scan_number()'s state machine, materializes
token_buffer in one copy (substituting the locale decimal point exactly as
scan_number() does), advances the adapter, and reuses the shared
convert_number() tail. On anything it does not recognize as a well-formed
number it makes no state change and returns token_type::uninitialized, so
the caller falls back to scan_number(), which then produces the exact
diagnostic. Errors and their positions are therefore unchanged.

The conversion tail is factored out of scan_number() into convert_number()
so both scanners share it; the fast path is selected by tag dispatch on the
existing bulk_scan capability, so streaming/wide/user adapters are
unaffected.

Measured on pointer input, g++ 13 -O3:
  - integers: parse +65%, accept +98%
  - floats:   parse +39%, accept +70%

Verified: 2,000,000 randomized number documents (including overflow-range
integers, long digit strings and %.17g doubles) parse identically via the
contiguous path and the streaming byte path, matching value, type and
round-trip text; the locale suite and existing parser/lexer/conversions/
deserialization tests pass; a new "lexer number fast path" test checks
contiguous-vs-streaming parity, token classification, and that malformed
numbers are rejected identically. Pure C++11, no intrinsics.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AXcDtEma2PjxgmPS9cQGzA
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-07-20 09:51:17 +00:00

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// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++ (supporting code)
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
#include "doctest_compatibility.h"
#define JSON_TESTS_PRIVATE
#include <nlohmann/json.hpp>
using nlohmann::json;
#include <sstream> // stringstream
#include <string> // string
#include <vector> // vector
namespace
{
// shortcut to scan a string literal
json::lexer::token_type scan_string(const char* s, bool ignore_comments = false);
json::lexer::token_type scan_string(const char* s, const bool ignore_comments)
{
auto ia = nlohmann::detail::input_adapter(s);
return nlohmann::detail::lexer<json, decltype(ia)>(std::move(ia), ignore_comments).scan(); // NOLINT(hicpp-move-const-arg,performance-move-const-arg)
}
} // namespace
std::string get_error_message(const char* s, bool ignore_comments = false); // NOLINT(misc-use-internal-linkage)
std::string get_error_message(const char* s, const bool ignore_comments)
{
auto ia = nlohmann::detail::input_adapter(s);
auto lexer = nlohmann::detail::lexer<json, decltype(ia)>(std::move(ia), ignore_comments); // NOLINT(hicpp-move-const-arg,performance-move-const-arg)
lexer.scan();
return lexer.get_error_message();
}
TEST_CASE("lexer class")
{
SECTION("scan")
{
SECTION("structural characters")
{
CHECK((scan_string("[") == json::lexer::token_type::begin_array));
CHECK((scan_string("]") == json::lexer::token_type::end_array));
CHECK((scan_string("{") == json::lexer::token_type::begin_object));
CHECK((scan_string("}") == json::lexer::token_type::end_object));
CHECK((scan_string(",") == json::lexer::token_type::value_separator));
CHECK((scan_string(":") == json::lexer::token_type::name_separator));
}
SECTION("literal names")
{
CHECK((scan_string("null") == json::lexer::token_type::literal_null));
CHECK((scan_string("true") == json::lexer::token_type::literal_true));
CHECK((scan_string("false") == json::lexer::token_type::literal_false));
}
SECTION("numbers")
{
CHECK((scan_string("0") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("1") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("2") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("3") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("4") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("5") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("6") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("7") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("8") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("9") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("-0") == json::lexer::token_type::value_integer));
CHECK((scan_string("-1") == json::lexer::token_type::value_integer));
CHECK((scan_string("1.1") == json::lexer::token_type::value_float));
CHECK((scan_string("-1.1") == json::lexer::token_type::value_float));
CHECK((scan_string("1E10") == json::lexer::token_type::value_float));
}
SECTION("whitespace")
{
// result is end_of_input, because not token is following
CHECK((scan_string(" ") == json::lexer::token_type::end_of_input));
CHECK((scan_string("\t") == json::lexer::token_type::end_of_input));
CHECK((scan_string("\n") == json::lexer::token_type::end_of_input));
CHECK((scan_string("\r") == json::lexer::token_type::end_of_input));
CHECK((scan_string(" \t\n\r\n\t ") == json::lexer::token_type::end_of_input));
}
}
SECTION("token_type_name")
{
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::uninitialized)) == "<uninitialized>"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::literal_true)) == "true literal"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::literal_false)) == "false literal"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::literal_null)) == "null literal"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::value_string)) == "string literal"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::value_unsigned)) == "number literal"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::value_integer)) == "number literal"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::value_float)) == "number literal"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::begin_array)) == "'['"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::begin_object)) == "'{'"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::end_array)) == "']'"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::end_object)) == "'}'"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::name_separator)) == "':'"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::value_separator)) == "','"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::parse_error)) == "<parse error>"));
CHECK((std::string(json::lexer::token_type_name(json::lexer::token_type::end_of_input)) == "end of input"));
}
SECTION("parse errors on first character")
{
for (int c = 1; c < 128; ++c)
{
// create string from the ASCII code
const auto s = std::string(1, static_cast<char>(c));
// store scan() result
const auto res = scan_string(s.c_str());
CAPTURE(s)
switch (c)
{
// single characters that are valid tokens
case ('['):
case (']'):
case ('{'):
case ('}'):
case (','):
case (':'):
case ('0'):
case ('1'):
case ('2'):
case ('3'):
case ('4'):
case ('5'):
case ('6'):
case ('7'):
case ('8'):
case ('9'):
{
CHECK((res != json::lexer::token_type::parse_error));
break;
}
// whitespace
case (' '):
case ('\t'):
case ('\n'):
case ('\r'):
{
CHECK((res == json::lexer::token_type::end_of_input));
break;
}
// anything else is not expected
default:
{
CHECK((res == json::lexer::token_type::parse_error));
break;
}
}
}
}
SECTION("very large string")
{
// strings larger than 1024 bytes yield a resize of the lexer's yytext buffer
std::string s("\"");
s += std::string(2048, 'x');
s += "\"";
CHECK((scan_string(s.c_str()) == json::lexer::token_type::value_string));
}
SECTION("fail on comments")
{
CHECK((scan_string("/", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/", false) == "invalid literal");
CHECK((scan_string("/!", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/!", false) == "invalid literal");
CHECK((scan_string("/*", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/*", false) == "invalid literal");
CHECK((scan_string("/**", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/**", false) == "invalid literal");
CHECK((scan_string("//", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("//", false) == "invalid literal");
CHECK((scan_string("/**/", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/**/", false) == "invalid literal");
CHECK((scan_string("/** /", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/** /", false) == "invalid literal");
CHECK((scan_string("/***/", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/***/", false) == "invalid literal");
CHECK((scan_string("/* true */", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/* true */", false) == "invalid literal");
CHECK((scan_string("/*/**/", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/*/**/", false) == "invalid literal");
CHECK((scan_string("/*/* */", false) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/*/* */", false) == "invalid literal");
}
SECTION("ignore comments")
{
CHECK((scan_string("/", true) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/", true) == "invalid comment; expecting '/' or '*' after '/'");
CHECK((scan_string("/!", true) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/!", true) == "invalid comment; expecting '/' or '*' after '/'");
CHECK((scan_string("/*", true) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/*", true) == "invalid comment; missing closing '*/'");
CHECK((scan_string("/**", true) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/**", true) == "invalid comment; missing closing '*/'");
CHECK((scan_string("//", true) == json::lexer::token_type::end_of_input));
CHECK((scan_string("/**/", true) == json::lexer::token_type::end_of_input));
CHECK((scan_string("/** /", true) == json::lexer::token_type::parse_error));
CHECK(get_error_message("/** /", true) == "invalid comment; missing closing '*/'");
CHECK((scan_string("/***/", true) == json::lexer::token_type::end_of_input));
CHECK((scan_string("/* true */", true) == json::lexer::token_type::end_of_input));
CHECK((scan_string("/*/**/", true) == json::lexer::token_type::end_of_input));
CHECK((scan_string("/*/* */", true) == json::lexer::token_type::end_of_input));
CHECK((scan_string("//\n//\n", true) == json::lexer::token_type::end_of_input));
CHECK((scan_string("/**//**//**/", true) == json::lexer::token_type::end_of_input));
}
}
TEST_CASE("lexer number fast path")
{
// The contiguous fast path (used for pointer/string input) must agree with
// the streaming byte path (used for std::istream) on token type, numeric
// value, and round-trip text for every well-formed number, and reject the
// same malformed numbers with the same message.
SECTION("contiguous vs streaming parity")
{
const std::vector<std::string> numbers =
{
"0", "-0", "1", "-1", "42", "-42", "10", "100", "1234567890",
"0.0", "-0.0", "3.14", "-3.14", "0.5", "-0.001", "123.456789",
"1e0", "1E0", "1e10", "1e-10", "1e+10", "1.5e3", "-2.5E-4",
"9223372036854775807", // INT64_MAX -> unsigned
"9223372036854775808", // INT64_MAX + 1 -> unsigned
"18446744073709551615", // UINT64_MAX -> unsigned
"18446744073709551616", // UINT64_MAX + 1 -> float
"-9223372036854775808", // INT64_MIN -> integer
"-9223372036854775809", // INT64_MIN - 1 -> float
"123456789012345678901234567890", // huge -> float
"0.30000000000000004", "2.2250738585072014e-308", "1e308"
};
for (const auto& n : numbers)
{
const std::string doc = "[" + n + "]";
// contiguous fast path
const json a = json::parse(doc);
// streaming byte path
std::stringstream ss(doc);
const json b = json::parse(ss);
CAPTURE(n);
CHECK(a == b);
CHECK(a.dump() == b.dump());
CHECK(a[0].type() == b[0].type());
}
}
SECTION("token type classification")
{
CHECK((scan_string("0") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("-1") == json::lexer::token_type::value_integer));
CHECK((scan_string("1.5") == json::lexer::token_type::value_float));
CHECK((scan_string("1e5") == json::lexer::token_type::value_float));
CHECK((scan_string("18446744073709551615") == json::lexer::token_type::value_unsigned));
CHECK((scan_string("18446744073709551616") == json::lexer::token_type::value_float));
CHECK((scan_string("-9223372036854775808") == json::lexer::token_type::value_integer));
CHECK((scan_string("-9223372036854775809") == json::lexer::token_type::value_float));
}
SECTION("malformed numbers are rejected identically")
{
for (const char* bad :
{"-", "1.", "1e", "1e+", "1.2e", "01", "-01", "1..2", "1.2.3"
})
{
CAPTURE(bad);
// the contiguous fast path must decline and let the byte path report
const std::string doc = std::string("[") + bad + "]";
CHECK_FALSE(json::accept(doc));
std::stringstream ss(doc);
CHECK_FALSE(json::accept(ss));
}
}
}
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