daw_count_digits.h

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// Copyright (c) Darrell Wright
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/beached/daw_json_link
//
 
#pragma once
 
#include "version.h"
 
#include <daw/daw_attributes.h>
#include <daw/daw_cxmath.h>
#include <daw/daw_simple_array.h>
#include <daw/daw_uint_buffer.h>
 
#include <cstdint>
 
namespace daw::json {
  inline namespace DAW_JSON_VER {
    namespace json_details {
      inline constexpr auto is_digit =
        []( char c ) DAW_JSON_CPP23_STATIC_CALL_OP -> daw::UInt8 {
        return static_cast<unsigned>( static_cast<unsigned char>( c ) ) -
                     static_cast<unsigned>(
                       static_cast<unsigned char>( '0' ) ) <
                   10U
                 ? daw::UInt8{ 0 }
                 : daw::UInt8{ 0xFFU };
      };
 
      template<typename Predicate>
      DAW_ATTRIB_FLATINLINE DAW_ATTRIB_NONNULL() inline constexpr std::int32_t
      count_4digits( char const * first, Predicate pred ) {
        daw::simple_array<daw::UInt8, 4> const buff{
          pred( first[3] ), pred( first[2] ), pred( first[2] ),
          pred( first[1] ) };
        auto const v = DAW_BIT_CAST( std::uint32_t, buff );
        if( v != 0 ) {
          auto result = daw::cxmath::count_leading_zeroes( v );
          result /= 8;
          return static_cast<std::int32_t>( result );
        }
        return -1;
      }
 
      template<typename Predicate>
      DAW_ATTRIB_FLATINLINE DAW_ATTRIB_NONNULL() inline constexpr std::int32_t
      count_8digits( char const * first, Predicate pred ) {
        daw::simple_array<daw::UInt8, 8> const buff{
          pred( first[7] ), pred( first[6] ), pred( first[5] ),
          pred( first[4] ), pred( first[3] ), pred( first[2] ),
          pred( first[1] ), pred( first[0] ) };
 
        auto const v = DAW_BIT_CAST( std::uint64_t, buff );
        if( v != 0 ) {
          auto result = daw::cxmath::count_leading_zeroes( v );
          result /= 8;
          return static_cast<std::int32_t>( result );
        }
        return -1;
      }
 
      template<typename CharT>
      DAW_ATTRIB_FLATTEN DAW_ATTRIB_RET_NONNULL
      DAW_ATTRIB_NONNULL( ) 
      inline constexpr CharT *count_digits(
        CharT *first, CharT *last ) {
        while( DAW_LIKELY( last - first >= 8 ) ) {
          auto const v = count_8digits( first, is_digit );
          if( v >= 0 ) {
            return first + v;
          }
          first += 8;
        }
        while( last - first >= 4 ) {
          auto const v = count_4digits( first, is_digit );
          if( v >= 0 ) {
            return first + v;
          }
          first += 4;
        }
 
        while( first != last ) {
          if( static_cast<unsigned>( *first ) -
                static_cast<unsigned>( static_cast<unsigned char>( '0' ) ) >=
              10U ) {
            return first;
          }
          ++first;
        }
        return first;
      }
    } // namespace json_details
  } // namespace DAW_JSON_VER
} // namespace daw::json