improve human readable floating point formatting (#331)

* improve human readable floating point formatting * fixup

Author: 9il

source/mir/bignum/decimal.d

@@ -240,7 +240,7 @@ struct Decimal(size_t maxSize64)
  size_t coefficientLength;
  static if (size_t.sizeof == 8)
  {
- if (__ctfe && size_t.sizeof == 8)
+ if (__ctfe)
  {
  uint[coefficient.data.length * 2] data;
  foreach (i; 0 .. coefficient.length)
@@ -280,9 +280,25 @@ struct Decimal(size_t maxSize64)
  {
  // try print decimal form without exponent
  // up to 6 digits exluding leading 0. or final .0
+ sizediff_t s = this.exponent + coefficientLength;
+ if (s <= 0)
+ {
+ //0.001....
+ //0.0001
+ //0.00001
+ //0.000001
+ if (s >= -2 || this.exponent >= -6)
+ {
+ w.put(zeros[!coefficient.sign .. -s + 2 + 1]);
+ w.put(buffer[$ - coefficientLength .. $]);
+ return;
+ }
+ }
+ else
  if (this.exponent >= 0)
  {
- if (this.exponent + coefficientLength <= 6)
+ ///dddddd.0
+ if (s <= 6)
  {
  buffer[$ - coefficientLength - 1] = '-';
  w.put(buffer[$ - coefficientLength - coefficient.sign .. $]);
@@ -291,25 +307,15 @@ struct Decimal(size_t maxSize64)
  }
  }
  else
- if (this.exponent < 0)
  {
- if (this.exponent >= -6 && coefficientLength <= 6)
+ ///dddddd.d....
+ if (s <= 6 || coefficientLength <= 6)
  {
- sizediff_t zerosLength = -this.exponent - coefficientLength;
- if (zerosLength >= 0)
- {
- w.put(zeros[!coefficient.sign .. zerosLength + 2 + 1]);
- w.put(buffer[$ - coefficientLength .. $]);
- return;
- }
- else
- {
- buffer[$ - coefficientLength - 1] = '-';
- w.put(buffer[$ - coefficientLength - coefficient.sign .. $ - coefficientLength - zerosLength]);
- buffer[$ - coefficientLength - zerosLength - 1] = '.';
- w.put(buffer[$ - coefficientLength - zerosLength - 1 .. $]);
- return;
- }
+ buffer[$ - coefficientLength - 1] = '-';
+ w.put(buffer[$ - coefficientLength - coefficient.sign .. $ - coefficientLength + s]);
+ buffer[$ - coefficientLength + s - 1] = '.';
+ w.put(buffer[$ - coefficientLength + s - 1 .. $]);
+ return;
  }
  }
  }
@@ -340,7 +346,8 @@ struct Decimal(size_t maxSize64)
  else
  enum N = 11;
 
- auto expLength = printSignedToTail(exponent, buffer[$ - N .. $], '\0');
+ // prints e+/-exponent
+ auto expLength = printSignedToTail(exponent, buffer[$ - N .. $], '+');
  buffer[$ - ++expLength] = 'e';
  w.put(buffer[$ - expLength .. $]);
  }

source/mir/format.d

@@ -718,11 +718,22 @@ unittest
  assert(stringBuf() << 0.000003 << getData == "0.000003");
  assert(stringBuf() << -3e-7 << getData == "-3e-7");
  assert(stringBuf() << 123456.0 << getData == "123456.0");
+ assert(stringBuf() << 123456.1 << getData == "123456.1");
  assert(stringBuf() << 12.3456 << getData == "12.3456");
  assert(stringBuf() << -0.123456 << getData == "-0.123456");
- assert(stringBuf() << 0.1234567 << getData == "1.234567e-1");
- assert(stringBuf() << -1234567.0 << getData == "-1.234567e6");
- assert(stringBuf() << 1234567890123.0 << getData == "1.234567890123e12");
+ assert(stringBuf() << 0.1234567 << getData == "0.1234567");
+ assert(stringBuf() << 0.01234567 << getData == "0.01234567");
+ assert(stringBuf() << 0.001234567 << getData == "0.001234567");
+ assert(stringBuf() << 1.234567e-4 << getData == "1.234567e-4");
+ assert(stringBuf() << -1234567.0 << getData == "-1.234567e+6");
+ assert(stringBuf() << 123456.7890123 << getData == "123456.7890123");
+ assert(stringBuf() << 1234567.890123 << getData == "1.234567890123e+6");
+ assert(stringBuf() << 1234567890123.0 << getData == "1.234567890123e+12");
+ assert(stringBuf() << 1234567890123.0 << getData == "1.234567890123e+12");
+ assert(stringBuf() << 0.30000000000000004 << getData == "0.30000000000000004");
+ assert(stringBuf() << 0.030000000000000002 << getData == "0.030000000000000002");
+ assert(stringBuf() << 0.0030000000000000005 << getData == "0.0030000000000000005");
+ assert(stringBuf() << 3.0000000000000003e-4 << getData == "3.0000000000000003e-4");
  assert(stringBuf() << +double.nan << getData == "nan");
  assert(stringBuf() << -double.nan << getData == "nan");
  assert(stringBuf() << +double.infinity << getData == "+inf");