Merge pull request #208 from cppalliance/206

Add signed and floating point literals

Author: mborland

doc/modules/ROOT/pages/literals.adoc

@@ -10,13 +10,17 @@ https://www.boost.org/LICENSE_1_0.txt
 
 == Description
 
-The library provides user-defined literal suffixes for concise construction of safe integer types.
+The library provides user-defined literal suffixes for concise construction of safe numeric types.
 The literals are defined in the `boost::safe_numbers::literals` namespace.
-The behavior of the literals depends on the type:
+The behavior of each literal depends on the target type:
 
 - For `_u8`, `_u16`, and `_u32`, the literal value is range-checked and throws `std::overflow_error` if the value exceeds the target type's maximum.
 - The `_u64` literal performs no range check since `unsigned long long` maps directly to `std::uint64_t` (statically verified).
-- The `_u128` literal parses a string representation and throws `std::overflow_error` on overflow or `std::invalid_argument` on invalid input.
+- The `_u128` literal accepts an integer-form token, parses the digit string, and throws `std::overflow_error` on overflow or `std::invalid_argument` on invalid input.
+- For `_i8`, `_i16`, `_i32`, and `_i64`, the literal magnitude is range-checked against the signed maximum and throws `std::overflow_error` if it exceeds it.
+  Negative values are formed by applying the wrapper's unary `operator-` to the positive literal: the expression `-42_i32` parses as `-(42_i32)`.
+- The `_i128` literal mirrors `_u128`: it parses an integer-form digit string into `int128_t` and throws on overflow or invalid input.
+- For `_f32` and `_f64`, the literal is taken as `long double` and range-checked against the target's maximum, throwing `std::overflow_error` on overflow.
 
 [source,c++]
 ----
@@ -30,6 +34,15 @@ constexpr auto operator ""_u32(unsigned long long int val) -> u32;
 constexpr auto operator ""_u64(unsigned long long int val) noexcept -> u64;
 constexpr auto operator ""_u128(const char* str) -> u128;
 
+constexpr auto operator ""_i8(unsigned long long int val) -> i8;
+constexpr auto operator ""_i16(unsigned long long int val) -> i16;
+constexpr auto operator ""_i32(unsigned long long int val) -> i32;
+constexpr auto operator ""_i64(unsigned long long int val) -> i64;
+constexpr auto operator ""_i128(const char* str) -> i128;
+
+constexpr auto operator ""_f32(long double val) -> f32;
+constexpr auto operator ""_f64(long double val) -> f64;
+
 } // namespace boost::safe_numbers::literals
 ----
 
@@ -56,7 +69,35 @@ constexpr auto operator ""_u128(const char* str) -> u128;
 
 | `_u128`
 | `u128`
-| Parses string; throws `std::overflow_error` on overflow, `std::invalid_argument` on invalid input
+| Parses digit string; throws `std::overflow_error` on overflow, `std::invalid_argument` on invalid input
+
+| `_i8`
+| `i8`
+| Throws `std::overflow_error` if magnitude > 127
+
+| `_i16`
+| `i16`
+| Throws `std::overflow_error` if magnitude > 32,767
+
+| `_i32`
+| `i32`
+| Throws `std::overflow_error` if magnitude > 2,147,483,647
+
+| `_i64`
+| `i64`
+| Throws `std::overflow_error` if magnitude > 9,223,372,036,854,775,807
+
+| `_i128`
+| `i128`
+| Parses digit string; throws `std::overflow_error` on overflow, `std::invalid_argument` on invalid input
+
+| `_f32`
+| `f32`
+| Throws `std::overflow_error` if value > `std::numeric_limits<float>::max()`
+
+| `_f64`
+| `f64`
+| Throws `std::overflow_error` if value > `std::numeric_limits<double>::max()`
 |===
 
 == Usage
@@ -72,14 +113,37 @@ constexpr auto b {1000_u16};
 constexpr auto c {100000_u32};
 constexpr auto d {9999999999_u64};
 constexpr auto e {340282366920938463463374607431768211455_u128};
+
+constexpr auto f {-42_i8};
+constexpr auto g {32767_i16};
+constexpr auto h {-2147483647_i32};
+constexpr auto i {9223372036854775807_i64};
+constexpr auto j {-170141183460469231731687303715884105727_i128};
+
+constexpr auto k {3.14_f32};
+constexpr auto l {2.718281828459045_f64};
 ----
 
 Literals are `constexpr` and can be used in compile-time contexts.
 When used in a `constexpr` context, an out-of-range value produces a compile error rather than a runtime exception.
 
+== Negative Signed Literals
+
+C++ user-defined literal operators never see a leading minus sign as part of their input.
+The expression `-42_i32` is parsed as `-(42_i32)`: the literal returns a positive `i32` and unary `operator-` on the wrapper produces the negative result.
+Because the literal's range check is against the positive maximum (`INT_MAX`), the asymmetric `INT_MIN` value is not directly expressible through the literal: writing `-128_i8` parses as `-(128_i8)`, and the inner literal throws because `128 > INT8_MAX`.
+Use direct construction for that one value:
+
+[source,c++]
+----
+constexpr auto min_i8 {i8{std::numeric_limits<std::int8_t>::min()}};
+----
+
+The same asymmetry applies to `_i16`, `_i32`, `_i64`, and `_i128`.
+
 == Examples
 
-.This https://github.com/boostorg/safe_numbers/blob/develop/examples/literals.cpp[example] demonstrates how to use user-defined literals with safe integer types.
+.This https://github.com/boostorg/safe_numbers/blob/develop/examples/literals.cpp[example] demonstrates how to use user-defined literals with safe numeric types.
 ====
 [source, c++]
 ----
@@ -93,6 +157,13 @@ Output:
 100000_u32 = 100000
 9999999999_u64 = 9999999999
 max_u128 = 340282366920938463463374607431768211455
+-42_i8  = -42
+max_i16 = 32767
+min+1_i32 = -2147483647
+max_i64 = 9223372036854775807
+min+1_i128 = -170141183460469231731687303715884105727
+pi_f32 = 3.14
+e_f64  = 2.71828
 100_u32 + 50_u32 = 150
 6_u32 * 7_u32    = 42
 constexpr 255_u8 = 255

examples/literals.cpp

@@ -3,10 +3,12 @@
 // https://www.boost.org/LICENSE_1_0.txt
 
 // This example demonstrates the use of user-defined literals for
-// constructing safe integer types. The literals provide a concise
+// constructing safe numeric types. The literals provide a concise
 // syntax and perform compile-time range checking when possible.
 
 #include <boost/safe_numbers/unsigned_integers.hpp>
+#include <boost/safe_numbers/signed_integers.hpp>
+#include <boost/safe_numbers/floats.hpp>
 #include <boost/safe_numbers/literals.hpp>
 #include <boost/safe_numbers/iostream.hpp>
 #include <iostream>
@@ -16,7 +18,7 @@ int main()
     using namespace boost::safe_numbers;
     using namespace boost::safe_numbers::literals;
 
-    // Construct safe integers using literal suffixes
+    // Construct safe unsigned integers using literal suffixes
     {
         constexpr auto a {42_u8};
         constexpr auto b {1000_u16};
@@ -31,6 +33,32 @@ int main()
         std::cout << "max_u128 = " << e << std::endl;
     }
 
+    // Signed integer literals. Negative values are formed by applying unary
+    // minus to a positive literal: -42_i32 parses as -(42_i32).
+    {
+        constexpr auto a {-42_i8};
+        constexpr auto b {32767_i16};
+        constexpr auto c {-2147483647_i32};
+        constexpr auto d {9223372036854775807_i64};
+        constexpr auto e {-170141183460469231731687303715884105727_i128};
+
+        std::cout << "-42_i8  = " << a << std::endl;
+        std::cout << "max_i16 = " << b << std::endl;
+        std::cout << "min+1_i32 = " << c << std::endl;
+        std::cout << "max_i64 = " << d << std::endl;
+        std::cout << "min+1_i128 = " << e << std::endl;
+    }
+
+    // Floating-point literals. The literal accepts a long double and is
+    // range-checked against the target type's maximum.
+    {
+        constexpr auto pi {3.14_f32};
+        constexpr auto e {2.718281828459045_f64};
+
+        std::cout << "pi_f32 = " << pi << std::endl;
+        std::cout << "e_f64  = " << e << std::endl;
+    }
+
     // Literals work naturally in expressions
     {
         const auto sum {100_u32 + 50_u32};
@@ -56,6 +84,8 @@ int main()
     //
     //   auto bad = 256_u8;    // throws std::overflow_error (> UINT8_MAX)
     //   auto bad = 70000_u16; // throws std::overflow_error (> UINT16_MAX)
+    //   auto bad = 128_i8;    // throws std::overflow_error (> INT8_MAX)
+    //   auto bad = 1.0e40_f32; // throws std::overflow_error (> FLT_MAX)
 
     return 0;
 }

include/boost/safe_numbers/detail/int128/detail/common_div.hpp

@@ -447,7 +447,7 @@ BOOST_SAFE_NUMBERS_DETAIL_INT128_HOST_DEVICE BOOST_SAFE_NUMBERS_DETAIL_INT128_FO
         return;
     }
 
-    #else
+    #endif
 
     if (rhs <= UINT32_MAX)
     {
@@ -467,8 +467,6 @@ BOOST_SAFE_NUMBERS_DETAIL_INT128_HOST_DEVICE BOOST_SAFE_NUMBERS_DETAIL_INT128_FO
         quotient = impl::from_words<T>(q);
         remainder = impl::from_words<T>(u);
     }
-
-    #endif
 }
 
 template <typename T>

include/boost/safe_numbers/detail/int128/detail/mini_from_chars.hpp

@@ -127,7 +127,6 @@ BOOST_SAFE_NUMBERS_DETAIL_INT128_HOST_DEVICE constexpr int from_chars_integer_im
 
 
     overflow_value /= unsigned_base;
-    overflow_value <<= 1;
     max_digit %= unsigned_base;
 
     // If the only character was a sign abort now
@@ -138,48 +137,56 @@ BOOST_SAFE_NUMBERS_DETAIL_INT128_HOST_DEVICE constexpr int from_chars_integer_im
 
     bool overflowed = false;
 
-    std::ptrdiff_t nc = last - next;
-    constexpr std::ptrdiff_t nd = std::numeric_limits<Integer>::digits10;
+    const std::ptrdiff_t nc = last - next;
 
+    // For bases 2..10 the first digits10 characters always fit in the unsigned
+    // target type without overflow, so the per-iteration check is unnecessary
+    // there: 10^digits10 <= 2^bits, and any base <= 10 packs no more value per
+    // digit than base 10. For bases above 10 the safe window is shorter than
+    // digits10 (e.g. only ~24 digits in base 36 fit in 128 bits), so the check
+    // must run on every iteration.
+    const std::ptrdiff_t nd {
+        base <= 10
+            ? static_cast<std::ptrdiff_t>(std::numeric_limits<Integer>::digits10)
+            : std::ptrdiff_t{0}
+    };
+
+    const std::ptrdiff_t fast_limit {nd < nc ? nd : nc};
+    std::ptrdiff_t i = 0;
+
+    for (; i < fast_limit; ++i)
     {
-        std::ptrdiff_t i = 0;
+        const auto current_digit = static_cast<Unsigned_Integer>(digit_from_char(*next));
 
-        for( ; i < nd && i < nc; ++i )
+        if (current_digit >= unsigned_base)
         {
-            // overflow is not possible in the first nd characters
+            break;
+        }
 
-            const auto current_digit = static_cast<Unsigned_Integer>(digit_from_char(*next));
+        result = static_cast<Unsigned_Integer>(result * unsigned_base + current_digit);
+        ++next;
+    }
 
-            if (current_digit >= unsigned_base)
-            {
-                break;
-            }
+    for (; i < nc; ++i)
+    {
+        const auto current_digit = static_cast<Unsigned_Integer>(digit_from_char(*next));
 
-            result = static_cast<Unsigned_Integer>(result * unsigned_base + current_digit);
-            ++next;
+        if (current_digit >= unsigned_base)
+        {
+            break;
         }
 
-        for( ; i < nc; ++i )
+        if (result < overflow_value || (result == overflow_value && current_digit <= max_digit))
         {
-            const auto current_digit = static_cast<Unsigned_Integer>(digit_from_char(*next));
-
-            if (current_digit >= unsigned_base)
-            {
-                break;
-            }
-
-            if (result < overflow_value || (result == overflow_value && current_digit <= max_digit))
-            {
-                result = static_cast<Unsigned_Integer>(result * unsigned_base + current_digit);
-            }
-            else
-            {
-                overflowed = true;
-                break;
-            }
-
-            ++next;
+            result = static_cast<Unsigned_Integer>(result * unsigned_base + current_digit);
         }
+        else
+        {
+            overflowed = true;
+            break;
+        }
+
+        ++next;
     }
 
     // Return the parsed value, adding the sign back if applicable