[libc][math][c23] Add {,u}fromfp{,x}{,f,l,f128} functions (llvm#86003)

Fixes llvm#85279.

cc @lntue

libc/config/linux/x86_64/entrypoints.txt

@@ -387,6 +387,12 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.frexp
     libc.src.math.frexpf
     libc.src.math.frexpl
+    libc.src.math.fromfp
+    libc.src.math.fromfpf
+    libc.src.math.fromfpl
+    libc.src.math.fromfpx
+    libc.src.math.fromfpxf
+    libc.src.math.fromfpxl
     libc.src.math.hypot
     libc.src.math.hypotf
     libc.src.math.ilogb
@@ -471,6 +477,12 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.trunc
     libc.src.math.truncf
     libc.src.math.truncl
+    libc.src.math.ufromfp
+    libc.src.math.ufromfpf
+    libc.src.math.ufromfpl
+    libc.src.math.ufromfpx
+    libc.src.math.ufromfpxf
+    libc.src.math.ufromfpxl
 )
 
 if(LIBC_TYPES_HAS_FLOAT128)
@@ -485,6 +497,8 @@ if(LIBC_TYPES_HAS_FLOAT128)
     libc.src.math.fminf128
     libc.src.math.fmodf128
     libc.src.math.frexpf128
+    libc.src.math.fromfpf128
+    libc.src.math.fromfpxf128
     libc.src.math.ilogbf128
     libc.src.math.ldexpf128
     libc.src.math.llogbf128
@@ -502,6 +516,8 @@ if(LIBC_TYPES_HAS_FLOAT128)
     libc.src.math.roundf128
     libc.src.math.sqrtf128
     libc.src.math.truncf128
+    libc.src.math.ufromfpf128
+    libc.src.math.ufromfpxf128
   )
 endif()
 

libc/docs/dev/undefined_behavior.rst

@@ -81,3 +81,11 @@ The C standard does not specify behavior for ``printf("%s", NULL)``. We will
 print the string literal ``(null)`` unless using the 
 ``LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS`` option described in :ref:`printf 
 behavior<printf_behavior>`.
+
+Unknown Math Rounding Direction
+-------------------------------
+The C23 standard states that if the value of the ``rnd`` argument of the
+``fromfp``, ``ufromfp``, ``fromfpx`` and ``ufromfpx`` functions is not equal to
+the value of a math rounding direction macro, the direction of rounding is
+unspecified. LLVM's libc chooses to use the ``FP_INT_TONEAREST`` rounding
+direction in this case.

libc/docs/math/index.rst

@@ -181,6 +181,22 @@ Basic Operations
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | frexpf128    | |check| | |check| |         | |check| |         |         |         |         |         |         |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfp       | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfpf      | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfpl      | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfpf128   | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfpx      | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfpxf     | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfpxl     | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| fromfpxf128  | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | ilogb        | |check| | |check| | |check| | |check| | |check| |         |         | |check| | |check| | |check| |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | ilogbf       | |check| | |check| | |check| | |check| | |check| |         |         | |check| | |check| | |check| |         |         |
@@ -339,6 +355,22 @@ Basic Operations
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | truncf128    | |check| | |check| |         | |check| |         |         |         |         |         |         |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfp      | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfpf     | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfpl     | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfpf128  | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfpx     | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfpxf    | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfpxl    | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| ufromfpxf128 | |check| |         |         |         |         |         |         |         |         |         |         |         |
++--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 
 
 Higher Math Functions

libc/include/llvm-libc-macros/math-macros.h

@@ -17,6 +17,12 @@
 #define FP_SUBNORMAL 3
 #define FP_NORMAL 4
 
+#define FP_INT_UPWARD 0
+#define FP_INT_DOWNWARD 1
+#define FP_INT_TOWARDZERO 2
+#define FP_INT_TONEARESTFROMZERO 3
+#define FP_INT_TONEAREST 4
+
 #define MATH_ERRNO 1
 #define MATH_ERREXCEPT 2
 

libc/spec/stdc.td

@@ -352,6 +352,12 @@ def StdC : StandardSpec<"stdc"> {
           Macro<"INFINITY">,
           Macro<"NAN">,
 
+          Macro<"FP_INT_UPWARD">,
+          Macro<"FP_INT_DOWNWARD">,
+          Macro<"FP_INT_TOWARDZERO">,
+          Macro<"FP_INT_TONEARESTFROMZERO">,
+          Macro<"FP_INT_TONEAREST">,
+
           Macro<"FP_ILOGB0">,
           Macro<"FP_ILOGBNAN">,
 
@@ -414,6 +420,26 @@ def StdC : StandardSpec<"stdc"> {
           FunctionSpec<"frexpl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntPtr>]>,
           GuardedFunctionSpec<"frexpf128", RetValSpec<Float128Type>, [ArgSpec<Float128Type>, ArgSpec<IntPtr>], "LIBC_TYPES_HAS_FLOAT128">,
 
+          FunctionSpec<"fromfp", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"fromfpf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"fromfpl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          GuardedFunctionSpec<"fromfpf128", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>], "LIBC_TYPES_HAS_FLOAT128">,
+
+          FunctionSpec<"fromfpx", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"fromfpxf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"fromfpxl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          GuardedFunctionSpec<"fromfpxf128", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>], "LIBC_TYPES_HAS_FLOAT128">,
+
+          FunctionSpec<"ufromfp", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"ufromfpf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"ufromfpl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          GuardedFunctionSpec<"ufromfpf128", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>], "LIBC_TYPES_HAS_FLOAT128">,
+
+          FunctionSpec<"ufromfpx", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"ufromfpxf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"ufromfpxl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>]>,
+          GuardedFunctionSpec<"ufromfpxf128", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>, ArgSpec<UnsignedIntType>], "LIBC_TYPES_HAS_FLOAT128">,
+
           FunctionSpec<"hypot", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<DoubleType>]>,
           FunctionSpec<"hypotf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<FloatType>]>,
 

libc/src/__support/FPUtil/NearestIntegerOperations.h

@@ -140,8 +140,9 @@ LIBC_INLINE T round(T x) {
   }
 }
 
-template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>
-LIBC_INLINE T round_using_current_rounding_mode(T x) {
+template <typename T>
+LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_floating_point_v<T>, T>
+round_using_specific_rounding_mode(T x, int rnd) {
   using StorageType = typename FPBits<T>::StorageType;
   FPBits<T> bits(x);
 
@@ -151,28 +152,30 @@ LIBC_INLINE T round_using_current_rounding_mode(T x) {
 
   bool is_neg = bits.is_neg();
   int exponent = bits.get_exponent();
-  int rounding_mode = quick_get_round();
 
   // If the exponent is greater than the most negative mantissa
   // exponent, then x is already an integer.
   if (exponent >= static_cast<int>(FPBits<T>::FRACTION_LEN))
     return x;
 
   if (exponent <= -1) {
-    switch (rounding_mode) {
-    case FE_DOWNWARD:
+    switch (rnd) {
+    case FP_INT_DOWNWARD:
       return is_neg ? T(-1.0) : T(0.0);
-    case FE_UPWARD:
+    case FP_INT_UPWARD:
       return is_neg ? T(-0.0) : T(1.0);
-    case FE_TOWARDZERO:
+    case FP_INT_TOWARDZERO:
       return is_neg ? T(-0.0) : T(0.0);
-    case FE_TONEAREST:
+    case FP_INT_TONEARESTFROMZERO:
+      if (exponent < -1)
+        return is_neg ? T(-0.0) : T(0.0); // abs(x) < 0.5
+      return is_neg ? T(-1.0) : T(1.0);   // abs(x) >= 0.5
+    case FP_INT_TONEAREST:
+    default:
       if (exponent <= -2 || bits.get_mantissa() == 0)
         return is_neg ? T(-0.0) : T(0.0); // abs(x) <= 0.5
       else
         return is_neg ? T(-1.0) : T(1.0); // abs(x) > 0.5
-    default:
-      __builtin_unreachable();
     }
   }
 
@@ -194,14 +197,19 @@ LIBC_INLINE T round_using_current_rounding_mode(T x) {
   StorageType trunc_is_odd =
       new_bits.get_mantissa() & (StorageType(1) << trim_size);
 
-  switch (rounding_mode) {
-  case FE_DOWNWARD:
+  switch (rnd) {
+  case FP_INT_DOWNWARD:
     return is_neg ? trunc_value - T(1.0) : trunc_value;
-  case FE_UPWARD:
+  case FP_INT_UPWARD:
     return is_neg ? trunc_value : trunc_value + T(1.0);
-  case FE_TOWARDZERO:
+  case FP_INT_TOWARDZERO:
     return trunc_value;
-  case FE_TONEAREST:
+  case FP_INT_TONEARESTFROMZERO:
+    if (trim_value >= half_value)
+      return is_neg ? trunc_value - T(1.0) : trunc_value + T(1.0);
+    return trunc_value;
+  case FP_INT_TONEAREST:
+  default:
     if (trim_value > half_value) {
       return is_neg ? trunc_value - T(1.0) : trunc_value + T(1.0);
     } else if (trim_value == half_value) {
@@ -214,11 +222,67 @@ LIBC_INLINE T round_using_current_rounding_mode(T x) {
     } else {
       return trunc_value;
     }
+  }
+}
+
+template <typename T>
+LIBC_INLINE cpp::enable_if_t<cpp::is_floating_point_v<T>, T>
+round_using_current_rounding_mode(T x) {
+  int rounding_mode = quick_get_round();
+
+  switch (rounding_mode) {
+  case FE_DOWNWARD:
+    return round_using_specific_rounding_mode(x, FP_INT_DOWNWARD);
+  case FE_UPWARD:
+    return round_using_specific_rounding_mode(x, FP_INT_UPWARD);
+  case FE_TOWARDZERO:
+    return round_using_specific_rounding_mode(x, FP_INT_TOWARDZERO);
+  case FE_TONEAREST:
+    return round_using_specific_rounding_mode(x, FP_INT_TONEAREST);
   default:
     __builtin_unreachable();
   }
 }
 
+template <bool IsSigned, typename T>
+LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_floating_point_v<T>, T>
+fromfp(T x, int rnd, unsigned int width) {
+  if (width == 0U)
+    return FPBits<T>::quiet_nan().get_val();
+
+  T rounded_value = round_using_specific_rounding_mode(x, rnd);
+
+  if constexpr (IsSigned) {
+    // T can't hold a finite number >= 2.0 * 2^EXP_BIAS.
+    if (width - 1 > FPBits<T>::EXP_BIAS)
+      return rounded_value;
+    if (rounded_value < -T(1U << (width - 1U)))
+      return FPBits<T>::quiet_nan().get_val();
+    if (rounded_value > T((1U << (width - 1U)) - 1U))
+      return FPBits<T>::quiet_nan().get_val();
+    return rounded_value;
+  }
+
+  if (rounded_value < T(0.0))
+    return FPBits<T>::quiet_nan().get_val();
+  // T can't hold a finite number >= 2.0 * 2^EXP_BIAS.
+  if (width <= FPBits<T>::EXP_BIAS && rounded_value > T(1U << width) - 1U)
+    return FPBits<T>::quiet_nan().get_val();
+  return rounded_value;
+}
+
+template <bool IsSigned, typename T>
+LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_floating_point_v<T>, T>
+fromfpx(T x, int rnd, unsigned int width) {
+  T rounded_value = fromfp<IsSigned>(x, rnd, width);
+  FPBits<T> bits(rounded_value);
+
+  if (!bits.is_nan() && rounded_value != x)
+    raise_except_if_required(FE_INEXACT);
+
+  return rounded_value;
+}
+
 namespace internal {
 
 template <typename F, typename I,

libc/src/math/CMakeLists.txt

@@ -127,6 +127,16 @@ add_math_entrypoint_object(frexpf)
 add_math_entrypoint_object(frexpl)
 add_math_entrypoint_object(frexpf128)
 
+add_math_entrypoint_object(fromfp)
+add_math_entrypoint_object(fromfpf)
+add_math_entrypoint_object(fromfpl)
+add_math_entrypoint_object(fromfpf128)
+
+add_math_entrypoint_object(fromfpx)
+add_math_entrypoint_object(fromfpxf)
+add_math_entrypoint_object(fromfpxl)
+add_math_entrypoint_object(fromfpxf128)
+
 add_math_entrypoint_object(hypot)
 add_math_entrypoint_object(hypotf)
 
@@ -267,3 +277,13 @@ add_math_entrypoint_object(trunc)
 add_math_entrypoint_object(truncf)
 add_math_entrypoint_object(truncl)
 add_math_entrypoint_object(truncf128)
+
+add_math_entrypoint_object(ufromfp)
+add_math_entrypoint_object(ufromfpf)
+add_math_entrypoint_object(ufromfpl)
+add_math_entrypoint_object(ufromfpf128)
+
+add_math_entrypoint_object(ufromfpx)
+add_math_entrypoint_object(ufromfpxf)
+add_math_entrypoint_object(ufromfpxl)
+add_math_entrypoint_object(ufromfpxf128)

libc/src/math/fromfp.h

@@ -0,0 +1,18 @@
+//===-- Implementation header for fromfp ------------------------*- 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_MATH_FROMFP_H
+#define LLVM_LIBC_SRC_MATH_FROMFP_H
+
+namespace LIBC_NAMESPACE {
+
+double fromfp(double x, int rnd, unsigned int width);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_FROMFP_H

libc/src/math/fromfpf.h

@@ -0,0 +1,18 @@
+//===-- Implementation header for fromfpf -----------------------*- 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_MATH_FROMFPF_H
+#define LLVM_LIBC_SRC_MATH_FROMFPF_H
+
+namespace LIBC_NAMESPACE {
+
+float fromfpf(float x, int rnd, unsigned int width);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_FROMFPF_H

libc/src/math/fromfpf128.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for fromfpf128 --------------------*- 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_MATH_FROMFPF128_H
+#define LLVM_LIBC_SRC_MATH_FROMFPF128_H
+
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE {
+
+float128 fromfpf128(float128 x, int rnd, unsigned int width);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_FROMFPF128_H