Fast double-to-ascii conversion.

src/grisu3.cc

Index: src/grisu3.cc
===================================================================
--- src/grisu3.cc	(revision 4092)
+++ src/grisu3.cc	(working copy)
@@ -74,8 +74,10 @@
 
 
 template<int alpha, int gamma>
-bool Grisu3<alpha, gamma>::grisu3(
-    double v, char* buffer, int* length, int* decimal_exponent) {
+bool Grisu3<alpha, gamma>::grisu3(double v,
+                                  char* buffer,
+                                  int* length,
+                                  int* decimal_exponent) {
   DiyFp w = Double(v).AsNormalizedDiyFp();
   // boundary_minus and boundary_plus are the boundaries between v and its
   // neighbors. Any number strictly between boundary_minus and boundary_plus
@@ -147,8 +149,12 @@
 //   numbers. If the precision is not enough to guarantee all the postconditions
 //   then false is returned. This usually happens rarely (~0.5%).
 template<int alpha, int gamma>
-bool Grisu3<alpha, gamma>::DigitGen(
-    DiyFp low, DiyFp w, DiyFp high, char* buffer, int* len, int* kappa) {
+bool Grisu3<alpha, gamma>::DigitGen(DiyFp low,
+                                    DiyFp w,
+                                    DiyFp high,
+                                    char* buffer,
+                                    int* len,
+                                    int* kappa) {
   ASSERT(low.e() == w.e() && w.e() == high.e());
   ASSERT(low.f() + 1 <= high.f() - 1);
   ASSERT(alpha <= w.e() && w.e() <= gamma);
@@ -177,8 +183,10 @@
 // furthermore receive the maximum number of bits 'number' has.
 // If number_bits == 0 then 0^-1 is returned
 // The number of bits must be <= 32.
-static void BiggestPowerTen(uint32_t number, int number_bits,
-                            uint32_t* power, int* exponent) {
+static void BiggestPowerTen(uint32_t number,
+                            int number_bits,
+                            uint32_t* power,
+                            int* exponent) {
   switch (number_bits) {
     case 32:
     case 31:
@@ -294,8 +302,12 @@
 // represents w. However we have to pay attention to low, high and w's
 // imprecision.
 template<int alpha, int gamma>
-bool Grisu3<alpha, gamma>::DigitGen_m60_m32(
-    DiyFp low, DiyFp w, DiyFp high, char* buffer, int* length, int* kappa) {
+bool Grisu3<alpha, gamma>::DigitGen_m60_m32(DiyFp low,
+                                            DiyFp w,
+                                            DiyFp high,
+                                            char* buffer,
+                                            int* length,
+                                            int* kappa) {
   // low, w and high are imprecise, but by less than one ulp (unit in the last
   // place).
   // If we remove (resp. add) 1 ulp from low (resp. high) we are certain that
@@ -321,8 +333,10 @@
   // We use too_high for the digit_generation and stop as soon as possible.
   // If we stop early we effectively round down.
   DiyFp one = DiyFp(static_cast<uint64_t>(1) << -w.e(), w.e());
-  uint32_t integrals = too_high.f() >> -one.e();        // Division by one.
-  uint64_t fractionals = too_high.f() & (one.f() - 1);  // Modulo by one.
+  // Division by one is a shift.
+  uint32_t integrals = static_cast<uint32_t>(too_high.f() >> -one.e());
+  // Modulo by one is an and.
+  uint64_t fractionals = too_high.f() & (one.f() - 1);
   uint32_t divider;
   int divider_exponent;
   BiggestPowerTen(integrals, DiyFp::kSignificandSize - (-one.e()),
@@ -332,7 +346,7 @@
   // Loop invariant: buffer = too_high / 10^kappa  (integer division)
   // The invariant holds for the first iteration: kappa has been initialized
   // with the divider exponent + 1. And the divider is the biggest power of ten
-  // that fits into the bits that had been reserved for the integrals.
+  // that is smaller than integrals.
   while (*kappa > 0) {
     int digit = integrals / divider;
     buffer[*length] = '0' + digit;
@@ -376,7 +390,8 @@
     unsafe_interval.set_e(unsafe_interval.e() + 1);  // Will be optimized out.
     one.set_f(one.f() >> 1);
     one.set_e(one.e() + 1);
-    int digit = fractionals >> -one.e();  // Integer division by one.
+    // Integer division by one.
+    int digit = static_cast<int>(fractionals >> -one.e());
     buffer[*length] = '0' + digit;
     (*length)++;
     fractionals &= one.f() - 1;  // Modulo by one.
@@ -402,10 +417,13 @@
 // Output: returns true on success.
 //    Modifies the generated digits in the buffer to approach (round towards) w.
 template<int alpha, int gamma>
-bool Grisu3<alpha, gamma>::RoundWeed(
-    char* buffer, int length, uint64_t distance_too_high_w,
-    uint64_t unsafe_interval, uint64_t rest, uint64_t ten_kappa,
-    uint64_t unit) {
+bool Grisu3<alpha, gamma>::RoundWeed(char* buffer,
+                                     int length,
+                                     uint64_t distance_too_high_w,
+                                     uint64_t unsafe_interval,
+                                     uint64_t rest,
+                                     uint64_t ten_kappa,
+                                     uint64_t unit) {
   uint64_t small_distance = distance_too_high_w - unit;
   uint64_t big_distance = distance_too_high_w + unit;
   // Let w- = too_high - big_distance, and
@@ -456,8 +474,7 @@
 }
 
 
-bool grisu3(double v,
-            char* buffer, int* sign, int* length, int* decimal_point) {
+bool grisu3(double v, char* buffer, int* sign, int* length, int* point) {
   ASSERT(v != 0);
   ASSERT(!Double(v).IsSpecial());
 
@@ -469,7 +486,7 @@
   }
   int decimal_exponent;
   bool result = Grisu3<-60, -32>::grisu3(v, buffer, length, &decimal_exponent);
-  *decimal_point = *length + decimal_exponent;
+  *point = *length + decimal_exponent;
   buffer[*length] = '\0';
   return result;
 }