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[libc][stdfix] Implement countlsfx functions in libc. #126597

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Merged
merged 21 commits into from
Feb 12, 2025
Merged

[libc][stdfix] Implement countlsfx functions in libc. #126597

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cbb321f
feat: implement template meta `countls`
krishna2803 Feb 1, 2025
cddf53e
chore: add `limits.h` header to CmakeLists.txt
krishna2803 Feb 1, 2025
bcccd52
add: `countlsfx` functions
krishna2803 Feb 1, 2025
647a16c
chore: add `padding_on_unsigned_fixed_point`
krishna2803 Feb 1, 2025
ca4d532
chore: add entrypoints
krishna2803 Feb 1, 2025
5c2894f
add: unit tests for `countlsfx` functions
krishna2803 Feb 1, 2025
519ae5d
chore: documentation update
krishna2803 Feb 1, 2025
e0acc36
chore: remove -Xclang flags and tests with padding
krishna2803 Feb 4, 2025
c31e539
nit: share loop for countlsfx and roundfx
krishna2803 Feb 4, 2025
9b499bc
fix: use `FXRep:TOTAL_LEN` to incoporate for `SIGN_LEN`
krishna2803 Feb 5, 2025
632a6d8
remove: `padding_on_unsigned_fixed_point.cpp`
krishna2803 Feb 5, 2025
475945d
chore: change `count leading zeros` to `count leading sign bits`
krishna2803 Feb 5, 2025
b146648
fix: ensure newline at end
krishna2803 Feb 5, 2025
659170d
style: clang-format
krishna2803 Feb 5, 2025
780fd3a
fix: buildbot failures
krishna2803 Feb 7, 2025
88e9b63
Merge branch 'main' into implement-countlsfx
krishna2803 Feb 10, 2025
c3c1c13
style: clang-format
krishna2803 Feb 10, 2025
ac10f17
Merge branch 'main' into implement-countlsfx
krishna2803 Feb 10, 2025
8790b2c
style: llvm coding standard
krishna2803 Feb 11, 2025
7a34ec1
chore: remove optimization options from maths functions (ref #126315)
krishna2803 Feb 11, 2025
958d51b
Merge branch 'main' into implement-countlsfx
krishna2803 Feb 11, 2025
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3 changes: 2 additions & 1 deletion libc/src/__support/fixed_point/fx_bits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -185,9 +185,10 @@ countls(T f) {
using BitType = typename FXRep::StorageType;
using FXBits = FXBits<T>;

if constexpr (FXRep::SIGN_LEN > 0)
if constexpr (FXRep::SIGN_LEN > 0) {
if (f < 0)
f = bit_not(f);
}
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@nickdesaulniers nickdesaulniers Feb 11, 2025

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ah, you had this correct before

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@krishna2803 krishna2803 Feb 11, 2025

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sorry if im missing something, but the doc says:

// Use braces on the outer `if` to avoid a potential dangling `else`
// situation.
if (isa<VarDecl>(D)) {
  if (shouldProcessAttr(A))
    handleAttr(A);
}

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@nickdesaulniers nickdesaulniers Feb 11, 2025

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oh, that's news to me. I guess because of constexpr we cant make it if (FXRep::SIGN_LEN > 0 && f < 0)... or could we?

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@krishna2803 krishna2803 Feb 11, 2025

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i'll just test it and see if it works!

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@krishna2803 krishna2803 Feb 11, 2025

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and it seems it doesn't..

// clang++ -std=c++20 -Wall hello.cpp -o hello
#include <iostream>

constexpr int x = 1;

int main() {
  int y;
  std::cin >> y;

  if constexpr (x > 0 && y > 4)
    std::cout << "foo bar";
}
hello.cpp:10:17: error: constexpr if condition is not a constant expression
  if constexpr (x > 0 && y > 4)
                ^~~~~~~~~~~~~~
hello.cpp:10:26: note: read of non-const variable 'y' is not allowed in a constant expression
  if constexpr (x > 0 && y > 4)
                         ^
hello.cpp:7:7: note: declared here
  int y;
      ^
1 error generated.

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@krishna2803 krishna2803 Feb 11, 2025

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same here:

In file included from /home/krishna/OpenSource/llvm-project/libc/src/stdfix/countlsr.cpp:11:
/home/krishna/OpenSource/llvm-project/libc/src/__support/fixed_point/fx_bits.h:188:17: error: constexpr if condition is not a constant expression
  188 |   if constexpr (FXRep::SIGN_LEN > 0 && f < 0)
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/krishna/OpenSource/llvm-project/libc/src/stdfix/countlsr.cpp:16:68: note: in instantiation of function template specialization '__llvm_libc_21_0_0_git::fixed_point::countls<_Fract>' requested here
   16 | LLVM_LIBC_FUNCTION(int, countlsr, (fract f)) { return fixed_point::countls(f); }
      |                                                                    ^
/home/krishna/OpenSource/llvm-project/libc/src/__support/fixed_point/fx_bits.h:188:40: note: function parameter 'f' with unknown value cannot be used in a constant expression
  188 |   if constexpr (FXRep::SIGN_LEN > 0 && f < 0)
      |                                        ^
/home/krishna/OpenSource/llvm-project/libc/src/__support/fixed_point/fx_bits.h:183:11: note: declared here
  183 | countls(T f) {
      |           ^
1 error generated.


BitType value_bits = FXBits(f).get_bits();
return cpp::countl_zero(value_bits) - FXRep::SIGN_LEN;
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2 changes: 1 addition & 1 deletion libc/test/src/stdfix/CMakeLists.txt
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Expand Up @@ -83,7 +83,7 @@ foreach(suffix IN ITEMS hr r lr hk k lk uhr ur ulr uhk uk ulk)
SRCS
countls${suffix}_test.cpp
COMPILE_OPTIONS
-O3
${libc_opt_high_flag}
DEPENDS
libc.src.stdfix.countls${suffix}
libc.src.__support.fixed_point.fx_rep
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9 changes: 3 additions & 6 deletions libc/test/src/stdfix/CountlsTest.h
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Expand Up @@ -36,21 +36,18 @@ template <typename T> class CountlsTest : public LIBC_NAMESPACE::testing::Test {
// bits according to ISO/IEC TR 18037.
EXPECT_EQ(is_signed ? 0 : FXRep::VALUE_LEN, func(min));

if (10 <= static_cast<int>(max)) {
if (10 <= static_cast<int>(max))
EXPECT_EQ(FXRep::INTEGRAL_LEN - 4, func(10));
}

if (static_cast<int>(min) <= -10) {
if (static_cast<int>(min) <= -10)
EXPECT_EQ(FXRep::INTEGRAL_LEN - 4, func(-10));
}

if constexpr (is_signed) {
EXPECT_EQ(FXRep::VALUE_LEN, func(-zero));
EXPECT_EQ(FXRep::VALUE_LEN, func(-eps));
EXPECT_EQ(FXRep::INTEGRAL_LEN + 1, func(-one_half));
if (FXRep::FRACTION_LEN >= 2) {
if (FXRep::FRACTION_LEN >= 2)
EXPECT_EQ(FXRep::INTEGRAL_LEN + 2, func(-one_fourth));
}
}
}
};
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