Grisu algorithms

README.md

@@ -12,7 +12,9 @@
 
 **dconv** is a header-only C++20 library for printing and parsing floating point numbers.
 
-Double to string conversion is done using the **Grisu2** algorithm, described by **Florian Loitsch** in its publication [Printing Floating-Point Numbers Quickly and Accurately with Integers](https://florian.loitsch.com/publications).
+Double to string conversion uses the **Grisu2** algorithm by default, described by **Florian Loitsch** in its publication [Printing Floating-Point Numbers Quickly and Accurately with Integers](https://florian.loitsch.com/publications).
+
+The **Grisu** and **Grisu3** algorithms from the same publication are also available. Grisu prints up to 18 digits without looking for the shortest output, Grisu2 prints the shortest output for about 99.9% of the doubles, and Grisu3 detects the remaining cases and falls back to `std::to_chars`.
 
 String to double conversion uses the **Eisel-Lemire** algorithm on the first 19 significant digits. Longer mantissas are bracketed between two Eisel-Lemire results; only when they disagree is the number rebuilt from the digits already read and passed to strtod. A stream is read once and never rewound; a buffer is only read again for mantissas longer than 19 digits.
 
@@ -72,6 +74,21 @@ char value[25];
 char* end = dconv::dtoa (value, -2.22507e-308);
 ```
 
+Each algorithm has its own header and namespace:
+
+```cpp
+#include <dconv/grisu3.hpp>
+
+char value[25];
+char* end = dconv::grisu3::dtoa (value, -2.22507e-308);
+```
+
+| Header | Function |
+| :--- | :--- |
+| `dconv/grisu3.hpp` | `dconv::grisu3::dtoa` |
+| `dconv/grisu2.hpp` | `dconv::grisu2::dtoa` |
+| `dconv/grisu.hpp` | `dconv::grisu::dtoa` |
+
 The parsing API can be used this way:
 
 ```cpp
@@ -95,7 +112,28 @@ std::istringstream in ("-2.22507e-308");
 bool ok = dconv::atod (in, value);
 ```
 
-`dtoa` needs a buffer of at least 25 bytes and returns the end of the written characters.
+A variant reads from a probe and stops on integers, so that integers can be kept as integers:
+
+```cpp
+#include <dconv/atod.hpp>
+
+double value;
+uint64_t significand;
+int64_t exponent;
+bool negative;
+std::error_code ec;
+
+dconv::StringProbe probe ("18446744073709551615");
+if (dconv::atod (probe, value, significand, exponent, negative, ec) == -1 && ec == dconv::Errc::NotDouble)
+{
+    // significand holds the integer, negative its sign.
+}
+```
+
+It returns `0` and the converted value for a real number, or `-1` with `Errc::NotDouble` for an integer without fraction nor exponent whose magnitude fits in 64 bits, or `-1` with `Errc::InvalidNumber` when parsing fails.
+`significand`, `exponent` and `negative` hold what was read until the end or the error.
+
+`dtoa` needs a buffer of at least 25 bytes (26 bytes for `grisu::dtoa`) and returns the end of the written characters.
 `atod` returns the end of the parsed characters, or `nullptr` on failure.
 The probe and stream overloads return `false` on failure and stop right after the number on success.
 They read the stream buffer directly: whitespaces are not skipped, the stream state is left unchanged and the characters read are consumed even on failure.

dconv/CMakeLists.txt

@@ -1,12 +1,19 @@
 cmake_minimum_required(VERSION 3.22.1)
 
 set(PUBLIC_HEADERS
+    include/dconv/error.hpp
     include/dconv/probe.hpp
-    include/dconv/diyfp.hpp
+    include/dconv/eisellemirepow.hpp
+    include/dconv/eisellemire.hpp
     include/dconv/atod.hpp
-    include/dconv/atodpow.hpp
+    include/dconv/digits.hpp
+    include/dconv/format.hpp
+    include/dconv/diyfp.hpp
+    include/dconv/grisupow.hpp
+    include/dconv/grisu.hpp
+    include/dconv/grisu2.hpp
+    include/dconv/grisu3.hpp
     include/dconv/dtoa.hpp
-    include/dconv/dtoapow.hpp
 )
 
 add_library(${PROJECT_NAME} INTERFACE)