Simplify powers-of-ten cache.

src/cached-powers.h

Index: src/cached-powers.h
diff --git a/src/cached-powers.h b/src/cached-powers.h
index 314ccca3c4539eb55f0de48522445a31934aad1b..0c7834317032aeee37ea71f301f119aca3a788e7 100644
--- a/src/cached-powers.h
+++ b/src/cached-powers.h
@@ -33,86 +33,10 @@
 namespace v8 {
 namespace internal {
 
-struct CachedPower {
-  uint64_t significand;
-  int16_t binary_exponent;
-  int16_t decimal_exponent;
-};
-
-// The following defines implement the interface between this file and the
-// generated 'powers_ten.h'.
-// GRISU_CACHE_NAME(1) contains all possible cached powers.
-// GRISU_CACHE_NAME(i) contains GRISU_CACHE_NAME(1) where only every 'i'th
-// element is kept. More formally GRISU_CACHE_NAME(i) contains the elements j*i
-// with 0 <= j < k with k such that j*k < the size of GRISU_CACHE_NAME(1).
-// The higher 'i' is the fewer elements we use.
-// Given that there are less elements, the exponent-distance between two
-// elements in the cache grows. The variable GRISU_CACHE_MAX_DISTANCE(i) stores
-// the maximum distance between two elements.
-#define GRISU_CACHE_STRUCT CachedPower
-#define GRISU_CACHE_NAME(i) kCachedPowers##i
-#define GRISU_CACHE_MAX_DISTANCE(i) kCachedPowersMaxDistance##i
-#define GRISU_CACHE_OFFSET kCachedPowerOffset
-#define GRISU_UINT64_C V8_2PART_UINT64_C
-// The following include imports the precompiled cached powers.
-#include "powers-ten.h"  // NOLINT
-
-static const double kD_1_LOG2_10 = 0.30102999566398114;  //  1 / lg(10)
-
-// We can't use a function since we reference variables depending on the 'i'.
-// This way the compiler is able to see at compile time that only one
-// cache-array variable is used and thus can remove all the others.
-#define COMPUTE_FOR_CACHE(i) \
-  if (!found && (gamma - alpha + 1 >= GRISU_CACHE_MAX_DISTANCE(i))) {   \
-    int kQ = DiyFp::kSignificandSize;                                   \
-    double k = ceiling((alpha - e + kQ - 1) * kD_1_LOG2_10);            \
-    int index = (GRISU_CACHE_OFFSET + static_cast<int>(k) - 1) / i + 1; \
-    cached_power = GRISU_CACHE_NAME(i)[index];                          \
-    found = true;                                                       \
-  }                                                                     \
-
-static void GetCachedPower(int e, int alpha, int gamma, int* mk, DiyFp* c_mk) {
-  // The following if statement should be optimized by the compiler so that only
-  // one array is referenced and the others are not included in the object file.
-  bool found = false;
-  CachedPower cached_power;
-  COMPUTE_FOR_CACHE(20);
-  COMPUTE_FOR_CACHE(19);
-  COMPUTE_FOR_CACHE(18);
-  COMPUTE_FOR_CACHE(17);
-  COMPUTE_FOR_CACHE(16);
-  COMPUTE_FOR_CACHE(15);
-  COMPUTE_FOR_CACHE(14);
-  COMPUTE_FOR_CACHE(13);
-  COMPUTE_FOR_CACHE(12);
-  COMPUTE_FOR_CACHE(11);
-  COMPUTE_FOR_CACHE(10);
-  COMPUTE_FOR_CACHE(9);
-  COMPUTE_FOR_CACHE(8);
-  COMPUTE_FOR_CACHE(7);
-  COMPUTE_FOR_CACHE(6);
-  COMPUTE_FOR_CACHE(5);
-  COMPUTE_FOR_CACHE(4);
-  COMPUTE_FOR_CACHE(3);
-  COMPUTE_FOR_CACHE(2);
-  COMPUTE_FOR_CACHE(1);
-  if (!found) {
-    UNIMPLEMENTED();
-    // Silence compiler warnings.
-    cached_power.significand = 0;
-    cached_power.binary_exponent = 0;
-    cached_power.decimal_exponent = 0;
-  }
-  *c_mk = DiyFp(cached_power.significand, cached_power.binary_exponent);
-  *mk = cached_power.decimal_exponent;
-  ASSERT((alpha <= c_mk->e() + e) && (c_mk->e() + e <= gamma));
-}
-#undef GRISU_REDUCTION
-#undef GRISU_CACHE_STRUCT
-#undef GRISU_CACHE_NAME
-#undef GRISU_CACHE_MAX_DISTANCE
-#undef GRISU_CACHE_OFFSET
-#undef GRISU_UINT64_C
+void GetCachedPowerForBinaryExponentRange(int min_exponent,
+                                          int max_exponent,
+                                          DiyFp* power,
+                                          int* decimal_exponent);
 
 } }  // namespace v8::internal