[libc++] Avoid including <cmath> in <compare> (#80418)

This reduces the time to include `<compare>` from 84ms to 36ms.

Author: philnik777

libcxx/include/__compare/strong_order.h

@@ -13,11 +13,14 @@
 #include <__compare/compare_three_way.h>
 #include <__compare/ordering.h>
 #include <__config>
+#include <__math/exponential_functions.h>
+#include <__math/traits.h>
 #include <__type_traits/conditional.h>
 #include <__type_traits/decay.h>
+#include <__type_traits/is_floating_point.h>
+#include <__type_traits/is_same.h>
 #include <__utility/forward.h>
 #include <__utility/priority_tag.h>
-#include <cmath>
 #include <cstdint>
 #include <limits>
 
@@ -66,27 +69,27 @@ struct __fn {
       return strong_ordering::greater;
     } else if (__t == __u) {
       if constexpr (numeric_limits<_Dp>::radix == 2) {
-        return std::signbit(__u) <=> std::signbit(__t);
+        return __math::signbit(__u) <=> __math::signbit(__t);
       } else {
         // This is bullet 3 of the IEEE754 algorithm, relevant
         // only for decimal floating-point;
         // see https://stackoverflow.com/questions/69068075/
-        if (__t == 0 || std::isinf(__t)) {
-          return std::signbit(__u) <=> std::signbit(__t);
+        if (__t == 0 || __math::isinf(__t)) {
+          return __math::signbit(__u) <=> __math::signbit(__t);
         } else {
           int __texp, __uexp;
-          (void)std::frexp(__t, &__texp);
-          (void)std::frexp(__u, &__uexp);
+          (void)__math::frexp(__t, &__texp);
+          (void)__math::frexp(__u, &__uexp);
           return (__t < 0) ? (__texp <=> __uexp) : (__uexp <=> __texp);
         }
       }
     } else {
       // They're unordered, so one of them must be a NAN.
       // The order is -QNAN, -SNAN, numbers, +SNAN, +QNAN.
-      bool __t_is_nan      = std::isnan(__t);
-      bool __u_is_nan      = std::isnan(__u);
-      bool __t_is_negative = std::signbit(__t);
-      bool __u_is_negative = std::signbit(__u);
+      bool __t_is_nan      = __math::isnan(__t);
+      bool __u_is_nan      = __math::isnan(__u);
+      bool __t_is_negative = __math::signbit(__t);
+      bool __u_is_negative = __math::signbit(__u);
       using _IntType =
           conditional_t< sizeof(__t) == sizeof(int32_t),
                          int32_t,

libcxx/include/__compare/weak_order.h

@@ -13,10 +13,12 @@
 #include <__compare/ordering.h>
 #include <__compare/strong_order.h>
 #include <__config>
+#include <__math/traits.h>
 #include <__type_traits/decay.h>
+#include <__type_traits/is_floating_point.h>
+#include <__type_traits/is_same.h>
 #include <__utility/forward.h>
 #include <__utility/priority_tag.h>
-#include <cmath>
 
 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
 #  pragma GCC system_header
@@ -51,10 +53,10 @@ struct __fn {
       return weak_ordering::greater;
     } else {
       // Otherwise, at least one of them is a NaN.
-      bool __t_is_nan      = std::isnan(__t);
-      bool __u_is_nan      = std::isnan(__u);
-      bool __t_is_negative = std::signbit(__t);
-      bool __u_is_negative = std::signbit(__u);
+      bool __t_is_nan      = __math::isnan(__t);
+      bool __u_is_nan      = __math::isnan(__u);
+      bool __t_is_negative = __math::signbit(__t);
+      bool __u_is_negative = __math::signbit(__u);
       if (__t_is_nan && __u_is_nan) {
         return (__u_is_negative <=> __t_is_negative);
       } else if (__t_is_nan) {

libcxx/include/compare

@@ -162,6 +162,7 @@ namespace std {
 #endif
 
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
+#  include <cmath>
 #  include <type_traits>
 #endif
 

libcxx/test/libcxx/transitive_includes/cxx23.csv

@@ -105,7 +105,6 @@ codecvt string
 codecvt tuple
 codecvt typeinfo
 codecvt version
-compare cmath
 compare cstddef
 compare cstdint
 compare limits

libcxx/test/libcxx/transitive_includes/cxx26.csv

@@ -105,7 +105,6 @@ codecvt string
 codecvt tuple
 codecvt typeinfo
 codecvt version
-compare cmath
 compare cstddef
 compare cstdint
 compare limits