[libc][NFC] Remove FPBits cast operator (#79142)

The semantics for casting can range from "bitcast" (same representation)
to "different representation", to "type promotion". Here we remove the
cast operator and force usage of `get_val` as the only function to get
the floating point value, making the intent clearer and more consistent.

Author: gchatelet

libc/src/__support/FPUtil/BasicOperations.h

@@ -21,7 +21,7 @@ template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>
 LIBC_INLINE T abs(T x) {
   FPBits<T> bits(x);
   bits.set_sign(Sign::POS);
-  return T(bits);
+  return bits.get_val();
 }
 
 template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>

libc/src/__support/FPUtil/DivisionAndRemainderOperations.h

@@ -86,7 +86,7 @@ LIBC_INLINE T remquo(T x, T y, int &q) {
   // then the conversion to native remainder value should be updated
   // appropriately and some directed tests added.
   T native_remainder(remainder);
-  T absy = T(ybits);
+  T absy = ybits.get_val();
   int cmp = remainder.mul2(1).cmp(normaly);
   if (cmp > 0) {
     q = q + 1;

libc/src/__support/FPUtil/FPBits.h

@@ -727,8 +727,6 @@ struct FPBits final : public internal::FPRep<get_fp_type<T>(), FPBits<T>> {
   // Floating-point conversions.
   LIBC_INLINE constexpr T get_val() const { return cpp::bit_cast<T>(bits); }
 
-  LIBC_INLINE constexpr explicit operator T() const { return get_val(); }
-
   // TODO: Use an uint32_t for 'biased_exp'.
   LIBC_INLINE static constexpr FPBits<T>
   create_value(Sign sign, StorageType biased_exp, StorageType mantissa) {

libc/src/__support/FPUtil/Hypot.h

@@ -111,7 +111,7 @@ LIBC_INLINE T hypot(T x, T y) {
   FPBits_t x_bits(x), y_bits(y);
 
   if (x_bits.is_inf() || y_bits.is_inf()) {
-    return T(FPBits_t::inf());
+    return FPBits_t::inf().get_val();
   }
   if (x_bits.is_nan()) {
     return x;
@@ -196,8 +196,8 @@ LIBC_INLINE T hypot(T x, T y) {
       if (out_exp >= FPBits_t::MAX_BIASED_EXPONENT) {
         if (int round_mode = quick_get_round();
             round_mode == FE_TONEAREST || round_mode == FE_UPWARD)
-          return T(FPBits_t::inf());
-        return T(FPBits_t::max_normal());
+          return FPBits_t::inf().get_val();
+        return FPBits_t::max_normal().get_val();
       }
     } else {
       // For denormal result, we simply move the leading bit of the result to
@@ -253,8 +253,8 @@ LIBC_INLINE T hypot(T x, T y) {
     ++out_exp;
     if (out_exp >= FPBits_t::MAX_BIASED_EXPONENT) {
       if (round_mode == FE_TONEAREST || round_mode == FE_UPWARD)
-        return T(FPBits_t::inf());
-      return T(FPBits_t::max_normal());
+        return FPBits_t::inf().get_val();
+      return FPBits_t::max_normal().get_val();
     }
   }
 

libc/src/__support/FPUtil/ManipulationFunctions.h

@@ -49,13 +49,13 @@ LIBC_INLINE T modf(T x, T &iptr) {
     return x;
   } else if (bits.is_inf()) {
     iptr = x;
-    return T(FPBits<T>::zero(bits.sign()));
+    return FPBits<T>::zero(bits.sign()).get_val();
   } else {
     iptr = trunc(x);
     if (x == iptr) {
       // If x is already an integer value, then return zero with the right
       // sign.
-      return T(FPBits<T>::zero(bits.sign()));
+      return FPBits<T>::zero(bits.sign()).get_val();
     } else {
       return x - iptr;
     }
@@ -66,7 +66,7 @@ template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>
 LIBC_INLINE T copysign(T x, T y) {
   FPBits<T> xbits(x);
   xbits.set_sign(FPBits<T>(y).sign());
-  return T(xbits);
+  return xbits.get_val();
 }
 
 template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>
@@ -103,12 +103,12 @@ LIBC_INLINE T logb(T x) {
   if (bits.is_zero()) {
     // TODO(Floating point exception): Raise div-by-zero exception.
     // TODO(errno): POSIX requires setting errno to ERANGE.
-    return T(FPBits<T>::inf(Sign::NEG));
+    return FPBits<T>::inf(Sign::NEG).get_val();
   } else if (bits.is_nan()) {
     return x;
   } else if (bits.is_inf()) {
     // Return positive infinity.
-    return T(FPBits<T>::inf());
+    return FPBits<T>::inf().get_val();
   }
 
   NormalFloat<T> normal(bits);
@@ -131,11 +131,11 @@ LIBC_INLINE T ldexp(T x, int exp) {
   // calculating the limit.
   int exp_limit = FPBits<T>::MAX_BIASED_EXPONENT + FPBits<T>::FRACTION_LEN + 1;
   if (exp > exp_limit)
-    return T(FPBits<T>::inf(bits.sign()));
+    return FPBits<T>::inf(bits.sign()).get_val();
 
   // Similarly on the negative side we return zero early if |exp| is too small.
   if (exp < -exp_limit)
-    return T(FPBits<T>::zero(bits.sign()));
+    return FPBits<T>::zero(bits.sign()).get_val();
 
   // For all other values, NormalFloat to T conversion handles it the right way.
   NormalFloat<T> normal(bits);

libc/src/__support/FPUtil/NearestIntegerOperations.h

@@ -41,11 +41,11 @@ LIBC_INLINE T trunc(T x) {
 
   // If the exponent is such that abs(x) is less than 1, then return 0.
   if (exponent <= -1)
-    return T(FPBits<T>::zero(bits.sign()));
+    return FPBits<T>::zero(bits.sign()).get_val();
 
   int trim_size = FPBits<T>::FRACTION_LEN - exponent;
   bits.set_mantissa((bits.get_mantissa() >> trim_size) << trim_size);
-  return T(bits);
+  return bits.get_val();
 }
 
 template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>
@@ -73,7 +73,7 @@ LIBC_INLINE T ceil(T x) {
 
   uint32_t trim_size = FPBits<T>::FRACTION_LEN - exponent;
   bits.set_mantissa((bits.get_mantissa() >> trim_size) << trim_size);
-  T trunc_value = T(bits);
+  T trunc_value = bits.get_val();
 
   // If x is already an integer, return it.
   if (trunc_value == x)
@@ -114,19 +114,19 @@ LIBC_INLINE T round(T x) {
 
   if (exponent == -1) {
     // Absolute value of x is greater than equal to 0.5 but less than 1.
-    return T(FPBits<T>::one(bits.sign()));
+    return FPBits<T>::one(bits.sign()).get_val();
   }
 
   if (exponent <= -2) {
     // Absolute value of x is less than 0.5.
-    return T(FPBits<T>::zero(bits.sign()));
+    return FPBits<T>::zero(bits.sign()).get_val();
   }
 
   uint32_t trim_size = FPBits<T>::FRACTION_LEN - exponent;
   bool half_bit_set =
       bool(bits.get_mantissa() & (StorageType(1) << (trim_size - 1)));
   bits.set_mantissa((bits.get_mantissa() >> trim_size) << trim_size);
-  T trunc_value = T(bits);
+  T trunc_value = bits.get_val();
 
   // If x is already an integer, return it.
   if (trunc_value == x)
@@ -180,7 +180,7 @@ LIBC_INLINE T round_using_current_rounding_mode(T x) {
   uint32_t trim_size = FPBits<T>::FRACTION_LEN - exponent;
   FPBits<T> new_bits = bits;
   new_bits.set_mantissa((bits.get_mantissa() >> trim_size) << trim_size);
-  T trunc_value = T(new_bits);
+  T trunc_value = new_bits.get_val();
 
   // If x is already an integer, return it.
   if (trunc_value == x)

libc/src/__support/FPUtil/NormalFloat.h

@@ -96,7 +96,7 @@ template <typename T> struct NormalFloat {
     // Max exponent is of the form 0xFF...E. That is why -2 and not -1.
     constexpr int MAX_EXPONENT_VALUE = (1 << FPBits<T>::EXP_LEN) - 2;
     if (biased_exponent > MAX_EXPONENT_VALUE) {
-      return T(FPBits<T>::inf(sign));
+      return FPBits<T>::inf(sign).get_val();
     }
 
     FPBits<T> result(T(0.0));
@@ -129,15 +129,15 @@ template <typename T> struct NormalFloat {
         // the overflow into the exponent.
         if (new_mantissa == ONE)
           result.set_biased_exponent(1);
-        return T(result);
+        return result.get_val();
       } else {
-        return T(result);
+        return result.get_val();
       }
     }
 
     result.set_biased_exponent(exponent + FPBits<T>::EXP_BIAS);
     result.set_mantissa(mantissa);
-    return T(result);
+    return result.get_val();
   }
 
 private:
@@ -250,16 +250,16 @@ template <> LIBC_INLINE NormalFloat<long double>::operator long double() const {
       } else {
         result.set_implicit_bit(0);
       }
-      return static_cast<long double>(result);
+      return result.get_val();
     } else {
-      return static_cast<long double>(result);
+      return result.get_val();
     }
   }
 
   result.set_biased_exponent(biased_exponent);
   result.set_mantissa(mantissa);
   result.set_implicit_bit(1);
-  return static_cast<long double>(result);
+  return result.get_val();
 }
 #endif // LIBC_LONG_DOUBLE_IS_X86_FLOAT80
 

libc/src/__support/FPUtil/generic/FMA.h

@@ -58,8 +58,8 @@ template <> LIBC_INLINE float fma<float>(float x, float y, float z) {
     // correct (when it matters).
     fputil::FPBits<double> t(
         (bit_prod.get_biased_exponent() >= bitz.get_biased_exponent())
-            ? ((double(bit_sum) - double(bit_prod)) - double(bitz))
-            : ((double(bit_sum) - double(bitz)) - double(bit_prod)));
+            ? ((bit_sum.get_val() - bit_prod.get_val()) - bitz.get_val())
+            : ((bit_sum.get_val() - bitz.get_val()) - bit_prod.get_val()));
 
     // Update sticky bits if t != 0.0 and the least (52 - 23 - 1 = 28) bits are
     // zero.
@@ -72,7 +72,7 @@ template <> LIBC_INLINE float fma<float>(float x, float y, float z) {
     }
   }
 
-  return static_cast<float>(static_cast<double>(bit_sum));
+  return static_cast<float>(bit_sum.get_val());
 }
 
 namespace internal {
@@ -257,7 +257,7 @@ template <> LIBC_INLINE double fma<double>(double x, double y, double z) {
         (round_mode == FE_DOWNWARD && prod_sign.is_pos())) {
       return FPBits::max_normal(prod_sign).get_val();
     }
-    return static_cast<double>(FPBits::inf(prod_sign));
+    return FPBits::inf(prod_sign).get_val();
   }
 
   // Remove hidden bit and append the exponent field and sign bit.

libc/src/__support/str_to_float.h

@@ -568,11 +568,11 @@ clinger_fast_path(ExpandedFloat<T> init_num,
                              ClingerConsts<T>::POWERS_OF_TEN_ARRAY[exp10]);
 
     // If the results are equal, then we don't need to use the rounding mode.
-    if (T(result) != -T(negative_result)) {
+    if (result.get_val() != -negative_result.get_val()) {
       FPBits lower_result;
       FPBits higher_result;
 
-      if (T(result) < -T(negative_result)) {
+      if (result.get_val() < -negative_result.get_val()) {
         lower_result = result;
         higher_result = negative_result;
       } else {
@@ -1194,7 +1194,7 @@ LIBC_INLINE StrToNumResult<T> strtofloatingpoint(const char *__restrict src) {
   // special 80 bit long doubles. Otherwise it should be inlined out.
   set_implicit_bit<T>(result);
 
-  return {T(result), index, error};
+  return {result.get_val(), index, error};
 }
 
 template <class T> LIBC_INLINE StrToNumResult<T> strtonan(const char *arg) {
@@ -1216,7 +1216,7 @@ template <class T> LIBC_INLINE StrToNumResult<T> strtonan(const char *arg) {
   }
 
   result = FPBits::build_quiet_nan(fputil::Sign::POS, nan_mantissa);
-  return {T(result), 0, error};
+  return {result.get_val(), 0, error};
 }
 
 } // namespace internal

libc/src/math/generic/exp.cpp

@@ -222,7 +222,7 @@ double set_exceptional(double x) {
     fputil::raise_except_if_required(FE_OVERFLOW);
   }
   // x is +inf or nan
-  return x + static_cast<double>(FPBits::inf());
+  return x + FPBits::inf().get_val();
 }
 
 } // namespace