[libc-commits] [libc] [libc][stdfix] Implement fxdivi functions (rdivi) (PR #154914)

[Shreeyash Pandey via libc-commits]

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@@ -224,6 +228,113 @@ idiv(T x, T y) {
   return static_cast<XType>(result);
 }
 
+LIBC_INLINE long accum nrstep(long accum d, long accum x0) {
+  auto v = x0 * (2.lk - (d * x0));
+  return v;
+}
+
+// Divide the two integers and return a fixed_point value
+//
+// For reference, see:
+// https://en.wikipedia.org/wiki/Division_algorithm#Newton%E2%80%93Raphson_division
+// https://stackoverflow.com/a/9231996
+
+template <typename XType> LIBC_INLINE constexpr XType divi(int n, int d) {
+  // If the value of the second operand of the / operator is zero, the
+  // behavior is undefined. Ref: ISO/IEC TR 18037:2008(E) p.g. 16
+  LIBC_CRASH_ON_VALUE(d, 0);
+
+  if (LIBC_UNLIKELY(n == 0)) {
+    return FXRep<XType>::ZERO();
+  }
+  auto is_power_of_two = [](int n) { return (n > 0) && ((n & (n - 1)) == 0); };
+  long accum max_val = static_cast<long accum>(FXRep<XType>::MAX());
+  long accum min_val = static_cast<long accum>(FXRep<XType>::MIN());
+
+  if (is_power_of_two(cpp::abs(d))) {
+    int k = cpp::countr_zero<uint32_t>(static_cast<uint32_t>(cpp::abs(d)));
+    constexpr int F = FXRep<XType>::FRACTION_LEN;
+    int64_t scaled_n = static_cast<int64_t>(n) << F;
+    int64_t res64 = scaled_n >> k;
+    constexpr int TotalBits = sizeof(XType) * 8;
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bojle wrote:

done

https://github.com/llvm/llvm-project/pull/154914