feat(libc): implement __powidf2

The H+8UBOwfScI import was a throwing stub (libcCyberUnknown08). It is
the NID of "__powidf2", the double-precision integer-power helper that
complements __powisf2.

core/libs/prx/libc/Export.cpp

@@ -26,12 +26,6 @@ int APS5_VABI _ZSt14_Atomic_assertPKcS0__nid_postfix() {
 }
 
 
-APS5_EXPORT("H+8UBOwfScI", libcCyberUnknown08);
-std::uint64_t APS5_VABI libcCyberUnknown08(void) {
-    NotImplemented_nid_no_patch("H+8UBOwfScI");
-    return 0;
-}
-
 APS5_EXPORT("H2e8t5ScQGc", libc___cxa_finalize);
 void APS5_VABI libc___cxa_finalize(void* dsoHandle) {
     CxaFinalize_nid_no_patch(dsoHandle);

core/libs/prx/libc/src/Math.cpp

@@ -376,6 +376,18 @@ float APS5_VABI __powisf2_nid_postfix(float base, int exponent) {
     }
     return reciprocal ? 1.0f / result : result;
 }
+double APS5_VABI __powidf2_nid_postfix(double base, int exponent) {
+    const bool reciprocal = exponent < 0;
+    double result = 1.0;
+    unsigned int magnitude = reciprocal ? 0u - static_cast<unsigned int>(exponent) : static_cast<unsigned int>(exponent);
+    while (magnitude != 0u) {
+        if ((magnitude & 1u) != 0u) result *= base;
+        magnitude >>= 1u;
+        if (magnitude == 0u) break;
+        base *= base;
+    }
+    return reciprocal ? 1.0 / result : result;
+}
 float APS5_VABI expf_nid_postfix(float x) { return std::exp(x); }
 float APS5_VABI exp2f_nid_postfix(float x) { return std::exp2(x); }
 float APS5_VABI logf_nid_postfix(float x) { return std::log(x); }

core/libs/tests/GuestMath.cpp

@@ -70,6 +70,7 @@ double APS5_VABI lgamma_nid_postfix(double);
 float APS5_VABI logbf_nid_postfix(float);
 double APS5_VABI exp2_nid_postfix(double);
 float APS5_VABI __powisf2_nid_postfix(float, int);
+double APS5_VABI __powidf2_nid_postfix(double, int);
 double APS5_VABI ldexp_nid_postfix(double, int);
 double APS5_VABI scalbn_nid_postfix(double, int);
 float APS5_VABI scalbnf_nid_postfix(float, int);
@@ -869,6 +870,21 @@ int main() {
     Require(std::signbit(__powisf2_nid_postfix(-0.0f, 3)));
     Require(std::isinf(__powisf2_nid_postfix(-0.0f, -3)) && std::signbit(__powisf2_nid_postfix(-0.0f, -3)));
     Require(__powisf2_nid_postfix(2.0f, -127) == 0x1p-127f);
+    Require(__powidf2_nid_postfix(2.0, 10) == 1024.0);
+    Require(__powidf2_nid_postfix(2.0, -10) == 0.0009765625);
+    Require(__powidf2_nid_postfix(-2.0, 3) == -8.0);
+    Require(__powidf2_nid_postfix(-2.0, -3) == -0.125);
+    Require(__powidf2_nid_postfix(-2.0, 4) == 16.0);
+    Require(__powidf2_nid_postfix(0.0, 0) == 1.0);
+    Require(__powidf2_nid_postfix(std::numeric_limits<double>::quiet_NaN(), 0) == 1.0);
+    Require(std::isnan(__powidf2_nid_postfix(std::numeric_limits<double>::quiet_NaN(), 1)));
+    Require(__powidf2_nid_postfix(-1.0, std::numeric_limits<int>::min()) == 1.0);
+    Require(__powidf2_nid_postfix(-1.0, std::numeric_limits<int>::max()) == -1.0);
+    Require(__powidf2_nid_postfix(2.0, std::numeric_limits<int>::min()) == 0.0);
+    Require(std::isinf(__powidf2_nid_postfix(0.0, -1)));
+    Require(std::signbit(__powidf2_nid_postfix(-0.0, 3)));
+    Require(std::isinf(__powidf2_nid_postfix(-0.0, -3)) && std::signbit(__powidf2_nid_postfix(-0.0, -3)));
+    Require(__powidf2_nid_postfix(2.0, -127) == 0x1p-127);
     CheckHyperbolic();
     CheckSinhf();
     CheckAtanhf();