[libc][stdfix] Add round functions for fixed point types. (#81994)

Author: lntue

libc/config/linux/x86_64/entrypoints.txt

@@ -451,6 +451,18 @@ if(LIBC_COMPILER_HAS_FIXED_POINT)
     libc.src.stdfix.absr
     libc.src.stdfix.abslk
     libc.src.stdfix.abslr
+    libc.src.stdfix.roundhk
+    libc.src.stdfix.roundhr
+    libc.src.stdfix.roundk
+    libc.src.stdfix.roundr
+    libc.src.stdfix.roundlk
+    libc.src.stdfix.roundlr
+    libc.src.stdfix.rounduhk
+    libc.src.stdfix.rounduhr
+    libc.src.stdfix.rounduk
+    libc.src.stdfix.roundur
+    libc.src.stdfix.roundulk
+    libc.src.stdfix.roundulr
   )
 endif()
 

libc/docs/math/stdfix.rst

@@ -76,7 +76,7 @@ Fixed-point Arithmetics
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
 | rdivi         |                |             |               |            |                |             |                |             |               |            |                |             |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
-| round         |                |             |               |            |                |             |                |             |               |            |                |             |
+| round         | |check|        | |check|     | |check|       | |check|    | |check|        | |check|     | |check|        | |check|     | |check|       | |check|    | |check|        | |check|     |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
 | sqrt          |                |             |               |            |                |             |                |             |               |            |                |             |
 +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+

libc/spec/stdc_ext.td

@@ -31,6 +31,22 @@ def StdcExt : StandardSpec<"stdc_ext"> {
           GuardedFunctionSpec<"abshk", RetValSpec<ShortAccumType>, [ArgSpec<ShortAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
           GuardedFunctionSpec<"absk", RetValSpec<AccumType>, [ArgSpec<AccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
           GuardedFunctionSpec<"abslk", RetValSpec<LongAccumType>, [ArgSpec<LongAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+
+          GuardedFunctionSpec<"roundhr", RetValSpec<ShortFractType>, [ArgSpec<ShortFractType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"roundr", RetValSpec<FractType>, [ArgSpec<FractType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"roundlr", RetValSpec<LongFractType>, [ArgSpec<LongFractType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+
+          GuardedFunctionSpec<"roundhk", RetValSpec<ShortAccumType>, [ArgSpec<ShortAccumType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"roundk", RetValSpec<AccumType>, [ArgSpec<AccumType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"roundlk", RetValSpec<LongAccumType>, [ArgSpec<LongAccumType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+
+          GuardedFunctionSpec<"rounduhr", RetValSpec<UnsignedShortFractType>, [ArgSpec<UnsignedShortFractType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"roundur", RetValSpec<UnsignedFractType>, [ArgSpec<UnsignedFractType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"roundulr", RetValSpec<UnsignedLongFractType>, [ArgSpec<UnsignedLongFractType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+
+          GuardedFunctionSpec<"rounduhk", RetValSpec<UnsignedShortAccumType>, [ArgSpec<UnsignedShortAccumType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"rounduk", RetValSpec<UnsignedAccumType>, [ArgSpec<UnsignedAccumType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"roundulk", RetValSpec<UnsignedLongAccumType>, [ArgSpec<UnsignedLongAccumType>, ArgSpec<IntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
       ]
   >;
 

libc/src/__support/fixed_point/CMakeLists.txt

@@ -17,4 +17,5 @@ add_header_library(
     libc.include.llvm-libc-macros.stdfix_macros
     libc.src.__support.macros.attributes
     libc.src.__support.macros.optimization
+    libc.src.__support.CPP.bit
 )

libc/src/__support/fixed_point/fx_bits.h

@@ -10,6 +10,8 @@
 #define LLVM_LIBC_SRC___SUPPORT_FIXEDPOINT_FXBITS_H
 
 #include "include/llvm-libc-macros/stdfix-macros.h"
+#include "src/__support/CPP/bit.h"
+#include "src/__support/CPP/type_traits.h"
 #include "src/__support/macros/attributes.h"   // LIBC_INLINE
 #include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
 
@@ -19,6 +21,36 @@
 
 namespace LIBC_NAMESPACE::fixed_point {
 
+// Bit-wise operations are not available for fixed point types yet.
+template <typename T>
+LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_fixed_point_v<T>, T>
+bit_and(T x, T y) {
+  using BitType = typename FXRep<T>::StorageType;
+  BitType x_bit = cpp::bit_cast<BitType>(x);
+  BitType y_bit = cpp::bit_cast<BitType>(y);
+  // For some reason, bit_cast cannot deduce BitType from the input.
+  return cpp::bit_cast<T, BitType>(x_bit & y_bit);
+}
+
+template <typename T>
+LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_fixed_point_v<T>, T>
+bit_or(T x, T y) {
+  using BitType = typename FXRep<T>::StorageType;
+  BitType x_bit = cpp::bit_cast<BitType>(x);
+  BitType y_bit = cpp::bit_cast<BitType>(y);
+  // For some reason, bit_cast cannot deduce BitType from the input.
+  return cpp::bit_cast<T, BitType>(x_bit | y_bit);
+}
+
+template <typename T>
+LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_fixed_point_v<T>, T>
+bit_not(T x) {
+  using BitType = typename FXRep<T>::StorageType;
+  BitType x_bit = cpp::bit_cast<BitType>(x);
+  // For some reason, bit_cast cannot deduce BitType from the input.
+  return cpp::bit_cast<T, BitType>(~x_bit);
+}
+
 template <typename T> LIBC_INLINE constexpr T abs(T x) {
   using FXRep = FXRep<T>;
   if constexpr (FXRep::SIGN_LEN == 0)
@@ -30,6 +62,27 @@ template <typename T> LIBC_INLINE constexpr T abs(T x) {
   }
 }
 
+// Round-to-nearest, tie-to-(+Inf)
+template <typename T> LIBC_INLINE constexpr T round(T x, int n) {
+  using FXRep = FXRep<T>;
+  if (LIBC_UNLIKELY(n < 0))
+    n = 0;
+  if (LIBC_UNLIKELY(n >= FXRep::FRACTION_LEN))
+    return x;
+
+  T round_bit = FXRep::EPS() << (FXRep::FRACTION_LEN - n - 1);
+  // Check for overflow.
+  if (LIBC_UNLIKELY(FXRep::MAX() - round_bit < x))
+    return FXRep::MAX();
+
+  T all_ones = bit_not(FXRep::ZERO());
+
+  int shift = FXRep::FRACTION_LEN - n;
+  T rounding_mask =
+      (shift == FXRep::TOTAL_LEN) ? FXRep::ZERO() : (all_ones << shift);
+  return bit_and((x + round_bit), rounding_mask);
+}
+
 } // namespace LIBC_NAMESPACE::fixed_point
 
 #endif // LIBC_COMPILER_HAS_FIXED_POINT

libc/src/stdfix/CMakeLists.txt

@@ -16,3 +16,18 @@ foreach(suffix IN ITEMS hr r lr hk k lk)
       libc.src.__support.fixed_point.fx_bits
   )
 endforeach()
+
+foreach(suffix IN ITEMS hr r lr hk k lk uhr ur ulr uhk uk ulk)
+  add_entrypoint_object(
+    round${suffix}
+    HDRS
+      round${suffix}.h
+    SRCS
+      round${suffix}.cpp
+    COMPILE_OPTIONS
+      -O3
+      -ffixed-point
+    DEPENDS
+      libc.src.__support.fixed_point.fx_bits
+  )
+endforeach()

libc/src/stdfix/roundhk.cpp

@@ -0,0 +1,19 @@
+//===-- Implementation of roundhk function --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "roundhk.h"
+#include "src/__support/common.h"
+#include "src/__support/fixed_point/fx_bits.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(short accum, roundhk, (short accum x, int n)) {
+  return fixed_point::round(x, n);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdfix/roundhk.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for roundhk -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDFIX_ROUNDHK_H
+#define LLVM_LIBC_SRC_STDFIX_ROUNDHK_H
+
+#include "include/llvm-libc-macros/stdfix-macros.h"
+
+namespace LIBC_NAMESPACE {
+
+short accum roundhk(short accum x, int n);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDFIX_ROUNDHK_H

libc/src/stdfix/roundhr.cpp

@@ -0,0 +1,19 @@
+//===-- Implementation of roundhr function --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "roundhr.h"
+#include "src/__support/common.h"
+#include "src/__support/fixed_point/fx_bits.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(short fract, roundhr, (short fract x, int n)) {
+  return fixed_point::round(x, n);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdfix/roundhr.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for roundhr -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDFIX_ROUNDHR_H
+#define LLVM_LIBC_SRC_STDFIX_ROUNDHR_H
+
+#include "include/llvm-libc-macros/stdfix-macros.h"
+
+namespace LIBC_NAMESPACE {
+
+short fract roundhr(short fract x, int n);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDFIX_ROUNDHR_H

libc/src/stdfix/roundk.cpp

@@ -0,0 +1,19 @@
+//===-- Implementation of roundk function ---------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "roundk.h"
+#include "src/__support/common.h"
+#include "src/__support/fixed_point/fx_bits.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(accum, roundk, (accum x, int n)) {
+  return fixed_point::round(x, n);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdfix/roundk.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for roundk ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDFIX_ROUNDK_H
+#define LLVM_LIBC_SRC_STDFIX_ROUNDK_H
+
+#include "include/llvm-libc-macros/stdfix-macros.h"
+
+namespace LIBC_NAMESPACE {
+
+accum roundk(accum x, int n);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDFIX_ROUNDK_H

libc/src/stdfix/roundlk.cpp

@@ -0,0 +1,19 @@
+//===-- Implementation of roundlk function --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "roundlk.h"
+#include "src/__support/common.h"
+#include "src/__support/fixed_point/fx_bits.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(long accum, roundlk, (long accum x, int n)) {
+  return fixed_point::round(x, n);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdfix/roundlk.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for roundlk -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDFIX_ROUNDLK_H
+#define LLVM_LIBC_SRC_STDFIX_ROUNDLK_H
+
+#include "include/llvm-libc-macros/stdfix-macros.h"
+
+namespace LIBC_NAMESPACE {
+
+long accum roundlk(long accum x, int n);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDFIX_ROUNDLK_H

libc/src/stdfix/roundlr.cpp

@@ -0,0 +1,19 @@
+//===-- Implementation of roundlr function --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "roundlr.h"
+#include "src/__support/common.h"
+#include "src/__support/fixed_point/fx_bits.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(long fract, roundlr, (long fract x, int n)) {
+  return fixed_point::round(x, n);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdfix/roundlr.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for roundlr -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDFIX_ROUNDLR_H
+#define LLVM_LIBC_SRC_STDFIX_ROUNDLR_H
+
+#include "include/llvm-libc-macros/stdfix-macros.h"
+
+namespace LIBC_NAMESPACE {
+
+long fract roundlr(long fract x, int n);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDFIX_ROUNDLR_H

libc/src/stdfix/roundr.cpp

@@ -0,0 +1,19 @@
+//===-- Implementation of roundr function ---------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "roundr.h"
+#include "src/__support/common.h"
+#include "src/__support/fixed_point/fx_bits.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(fract, roundr, (fract x, int n)) {
+  return fixed_point::round(x, n);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdfix/roundr.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for roundr ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDFIX_ROUNDR_H
+#define LLVM_LIBC_SRC_STDFIX_ROUNDR_H
+
+#include "include/llvm-libc-macros/stdfix-macros.h"
+
+namespace LIBC_NAMESPACE {
+
+fract roundr(fract x, int n);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDFIX_ROUNDR_H