Fix dynamic rate step bracketing interval

CHANGELOG.md

@@ -1,8 +1,12 @@
+## 1.0.2
+
+- Fixed: The `find_bracketing_interval` function now supports extremely high rates, improving precision for very high XIRRs (over 1E300%). Dynamic step sizing ensures accurate results even at extreme rates.
+
 ## 1.0.1
 
-- Fix: Resolved an issue where calculating XIRR with an empty cash flow array returned 10. It now correctly returns 0.
+- Fixed: Resolved an issue where calculating XIRR with an empty cash flow array returned 10. It now correctly returns 0.
 
 ## 1.0.0 / 2024-07-03
 
-### Initial Release 
+### Initial Release
 

ext/fast_xirr/common.c

@@ -66,13 +66,12 @@ int find_bracketing_interval(CashFlow *cashflows, long long count, double *low,
     }
 
     // Extend the search range if no interval is found within the initial range
-    step = 10.0;
-    for (double rate = max_rate + step; rate <= 10000.0; rate += step) {
+    for (double rate = max_rate; rate <= 1e300; rate *= 1.5) {
         double npv_rate = npv(rate, cashflows, count, min_date);
 
         // Check if the function values at consecutive rates have opposite signs
         if (npv_min_rate * npv_rate < 0) {
-            *low = rate - step;
+            *low = rate / 1.5;
             *high = rate;
             return 1;
         }

spec/use_cases_spec.rb

@@ -35,14 +35,14 @@
     expect(result).to be_within(1e-6).of(22.35220616417055)
   end
 
-  it 'returns NaN for a good investment that cannot be annualized' do
+  it 'calculates xirr for an extremely good and unrealistic investment' do
     cashflows = [
       [-1000, Date.new(1985, 1, 1)],
       [6000, Date.new(1985, 1, 2)]
     ]
 
     result = FastXirr.calculate(cashflows: cashflows)
-    expect(result.nan?).to be true
+    expect(result).to be_within(1e-6).of(1.0597571969623571e+284)
   end
 
   it 'returns NaN for all negative cashflows' do