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Update cohort preservation charconv example
Closes: #1210
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-112
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‎doc/modules/ROOT/pages/cohorts.adoc‎

Lines changed: 68 additions & 108 deletions
Original file line numberDiff line numberDiff line change
@@ -29,115 +29,75 @@ Below is an example of how cohorts can be preserved if one so wishes.
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== Cohort Preserving `<charconv>` Example
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This example can be found in the `examples/` folder as https://github.com/cppalliance/decimal/blob/develop/examples/charconv_cohort_preservation.cpp[charconv_cohort_preservation.cpp].
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[source, c++]
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----
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// This file demonstrates the effects of cohorts and how to maintain them with <charconv>
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#include <boost/decimal/decimal32_t.hpp> // For the type decimal32_t
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#include <boost/decimal/charconv.hpp> // For decimal support for <charconv>
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#include <boost/decimal/iostream.hpp> // For decimal support for <iostream>
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#include <iostream>
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#include <array>
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#include <cstring>
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#include <string>
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static constexpr std::size_t N {7};
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// All the following decimal values will compare equal,
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// but since they have different numbers of 0s in the significand they will not be bitwise equal
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constexpr std::array<boost::decimal::decimal32_t, N> decimals = {
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boost::decimal::decimal32_t{3, 2},
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boost::decimal::decimal32_t{30, 1},
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boost::decimal::decimal32_t{300, 0},
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boost::decimal::decimal32_t{3000, -1},
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boost::decimal::decimal32_t{30000, -2},
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boost::decimal::decimal32_t{300000, -3},
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boost::decimal::decimal32_t{3000000, -4},
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};
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// These strings represent the same values as the constructed ones shown above
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constexpr std::array<const char*, N> strings = {
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"3e+02",
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"3.0e+02",
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"3.00e+02",
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"3.000e+02",
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"3.0000e+02",
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"3.00000e+02",
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"3.000000e+02",
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};
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int main()
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{
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using boost::decimal::decimal32_t;
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using boost::decimal::from_chars;
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using boost::decimal::chars_format;
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// In some instances we want to preserve the cohort of our values
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// In the above strings array all of these values compare equal,
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// but will NOT be bitwise equal once constructed.
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for (std::size_t i = 0; i < N; ++i)
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{
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decimal32_t string_val;
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const auto r_from = from_chars(strings[i], string_val, chars_format::cohort_preserving_scientific);
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if (!r_from)
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{
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// Unexpected failure
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return 1;
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}
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for (std::size_t j = 0; j < N; ++j)
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{
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// Now that we have constructed a value from string
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// we can compare it bitwise to all the members of the decimal array
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// to show the difference between operator== and bitwise equality
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//
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// All members of a cohort are supposed to compare equal with operator==,
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// and likewise will hash equal to
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std::uint32_t string_val_bits;
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std::uint32_t constructed_val_bits;
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std::memcpy(&string_val_bits, &string_val, sizeof(string_val_bits));
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std::memcpy(&constructed_val_bits, &decimals[j], sizeof(constructed_val_bits));
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if (string_val == decimals[j])
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{
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std::cout << "Values are equal and ";
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if (string_val_bits == constructed_val_bits)
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{
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std::cout << "bitwise equal.\n";
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}
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else
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{
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std::cout << "NOT bitwise equal.\n";
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}
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}
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}
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// The same chars_format option applies to to_chars which allows us to roundtrip the values
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char buffer[64] {};
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const auto r_to = to_chars(buffer, buffer + sizeof(buffer), string_val, chars_format::cohort_preserving_scientific);
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if (!r_to)
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{
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// Unexpected failure
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return 1;
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}
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*r_to.ptr = '\0'; // charconv does not null terminate per the C++ specification
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if (std::strcmp(strings[i], buffer) == 0)
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{
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std::cout << "Successful Roundtrip\n\n";
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}
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else
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{
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std::cout << "Failed\n\n";
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return 1;
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}
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}
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include::example$charconv_cohort_preservation.cpp[]
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----
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return 0;
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}
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Expected Output:
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----
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Values are equal and bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Successful Roundtrip of value: 3e+02
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Values are equal and NOT bitwise equal.
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Values are equal and bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Successful Roundtrip of value: 3.0e+02
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Successful Roundtrip of value: 3.00e+02
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Successful Roundtrip of value: 3.000e+02
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Successful Roundtrip of value: 3.0000e+02
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and bitwise equal.
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Values are equal and NOT bitwise equal.
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Successful Roundtrip of value: 3.00000e+02
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and NOT bitwise equal.
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Values are equal and bitwise equal.
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Successful Roundtrip of value: 3.000000e+02
143103
----

‎examples/charconv_cohort_preservation.cpp‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -39,9 +39,9 @@ constexpr std::array<const char*, N> strings = {
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int main()
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{
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using boost::decimal::decimal32_t;
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using boost::decimal::from_chars;
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using boost::decimal::chars_format;
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using boost::decimal::decimal32_t; // For type decimal32_t
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using boost::decimal::from_chars; // decimal specific from_chars
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using boost::decimal::chars_format; // chars_format enum with decimal specific option shown here
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// In some instances we want to preserve the cohort of our values
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// In the above strings array all of these values compare equal,
@@ -100,7 +100,7 @@ int main()
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if (std::strcmp(strings[i], buffer) == 0)
102102
{
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std::cout << "Successful Roundtrip\n\n";
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std::cout << "Successful Roundtrip of value: " << buffer << "\n\n";
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}
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else
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{

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