[libc] Specify rounding mode for strto[f|d] tests

The specified rounding mode will be used and restored
to what it was before the test ran.

Additionally, it moves ForceRoundingMode and RoundingMode

[libc] Specify rounding mode for strto[f|d] tests

The specified rounding mode will be used and restored
to what it was before the test ran.

Additionally, it moves ForceRoundingMode and RoundingMode
out of MPFRUtils to be used in more places.

Differential Revision: https://reviews.llvm.org/D129685

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[libc] apply formatting to tests

Apply the formatting rules that were applied to the libc/src directory
to the libc/test directory, as well as the files in libc/utils that are
included by the tests.

[libc] apply formatting to tests

Apply the formatting rules that were applied to the libc/src directory
to the libc/test directory, as well as the files in libc/utils that are
included by the tests. This does not include automated enforcement.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D116127

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[libc] apply new lint rules

This patch applies the lint rules described in the previous patch. There
was also a significant amount of effort put into manually fixing things,
since all of the templat

[libc] apply new lint rules

This patch applies the lint rules described in the previous patch. There
was also a significant amount of effort put into manually fixing things,
since all of the templated functions, or structs defined in /spec, were
not updated and had to be handled manually.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D114302

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[libc] fix strtof/d/ld NaN parsing

Fix the fact that previously strtof/d/ld would only accept a NaN as
having parentheses if the thing in the parentheses was a valid number,
now it will accept any c

[libc] fix strtof/d/ld NaN parsing

Fix the fact that previously strtof/d/ld would only accept a NaN as
having parentheses if the thing in the parentheses was a valid number,
now it will accept any combination of letters and numbers, but will only
put valid numbers in the mantissa.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D113790

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[libc] Correct rounding for hexadecimalStringToFloat with long inputs.

Update binaryExpTofloat so that it will round correctly for long inputs when converting hexadecimal strings to floating points.

[libc] Correct rounding for hexadecimalStringToFloat with long inputs.

Update binaryExpTofloat so that it will round correctly for long inputs when converting hexadecimal strings to floating points.

Differential Revision: https://reviews.llvm.org/D113815

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[libc] tweak strtof errno behavior

When strtof/d/ld return a subnormal number they may set errno to
ERANGE. This change makes this behavior more consistent by making any
decimal number converting to

[libc] tweak strtof errno behavior

When strtof/d/ld return a subnormal number they may set errno to
ERANGE. This change makes this behavior more consistent by making any
decimal number converting to a subnormal set errno to ERANGE. This
brings it in line with hexadecimals, which currently only set errno to
ERANGE if the number is truncated when converting to a subnormal.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D113626

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[libc] refactor atof string parsing

Split the code for parsing hexadecimal floating point numbers from the
code for parsing the decimal floating point numbers so that the parsing
can be faster for b

[libc] refactor atof string parsing

Split the code for parsing hexadecimal floating point numbers from the
code for parsing the decimal floating point numbers so that the parsing
can be faster for both of them.

This decreases the time for the benchmark in release mode by about 15%,
which noticeably beats GLibc.

Old version: 2.299s
New version: 1.893s
GLibc: 2.133s

Tests run by running the following command 10 times for each version:
time ~/llvm-project/build/bin/libc_str_to_float_comparison_test ~/parse-number-fxx-test-data/data/*

the parse-number-fxx-test-data-repository is here:
https://github.com/nigeltao/parse-number-fxx-test-data/tree/fe94de252c691900982050c8e7c503d1efd1299a

It's important to build llvm-libc in Release mode for accurate
performance comparisons against glibc (set -DCMAKE_BUILD_TYPE=Release in
your cmake).
You also have to build the libc_str_to_float_comparison_test target.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D113036

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[libc] add atof, strtof and strtod

Add the string to floating point conversion functions.
Long doubles aren't supported yet, but floats and doubles are. The
primary algorithm used is the Eisel-Lemir

[libc] add atof, strtof and strtod

Add the string to floating point conversion functions.
Long doubles aren't supported yet, but floats and doubles are. The
primary algorithm used is the Eisel-Lemire ParseNumberF64 algorithm,
with the Simple Decimal Conversion algorithm as backup.

Links for more information on the algorithms:

Number Parsing at a Gigabyte per Second, Software: Practice and
Experience 51 (8), 2021 (https://arxiv.org/abs/2101.11408)
https://nigeltao.github.io/blog/2020/eisel-lemire.html
https://nigeltao.github.io/blog/2020/parse-number-f64-simple.html

Differential Revision: https://reviews.llvm.org/D109261

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