Merge changes to reals formatting from master

1 files changed, 413 insertions, 454 deletions

diff --git a/source/tanya/format/package.d b/source/tanya/format/package.d
index 44c079c..70b32c7 100644
--- a/source/tanya/format/package.d
+++ b/source/tanya/format/package.d
@@ -17,11 +17,138 @@ module tanya.format;
 import tanya.container.string;
 import tanya.encoding.ascii;
 public import tanya.format.conv;
+import tanya.math;
 import tanya.memory.op;
 import tanya.meta.metafunction;
 import tanya.meta.trait;
 import tanya.range.array;
 
+// Integer and floating point to string conversion is based on stb_sprintf
+// written by Jeff Roberts.
+
+// Returns the last part of buffer with converted number.
+package(tanya) char[] integral2String(T)(T number, return ref char[21] buffer)
+if (isIntegral!T)
+{
+    // abs the integer.
+    ulong n64 = number < 0 ? -cast(long) number : number;
+
+    char* start = buffer[].ptr + buffer.sizeof - 1;
+
+    while (true)
+    {
+        // Do in 32-bit chunks (avoid lots of 64-bit divides even with constant
+        // denominators).
+        char* o = start - 8;
+        uint n;
+        if (n64 >= 100000000)
+        {
+            n = n64 % 100000000;
+            n64 /= 100000000;
+        }
+        else
+        {
+            n = cast(uint) n64;
+            n64 = 0;
+        }
+
+        while (n)
+        {
+            *--start = cast(char) (n % 10) + '0';
+            n /= 10;
+        }
+        // Ignore the leading zero if it was the last part of the integer.
+        if (n64 == 0)
+        {
+            if ((start[0] == '0')
+             && (start != (buffer[].ptr + buffer.sizeof -1)))
+            {
+                ++start;
+            }
+            break;
+        }
+        // Copy leading zeros if it wasn't the most significant part of the
+        // integer.
+        while (start != o)
+        {
+            *--start = '0';
+        }
+    }
+
+    // Get the length that we have copied.
+    uint l = cast(uint) ((buffer[].ptr + buffer.sizeof - 1) - start);
+    if (l == 0)
+    {
+        *--start = '0';
+        l = 1;
+    }
+    else if (number < 0) // Set the sign.
+    {
+        *--start = '-';
+        ++l;
+    }
+
+    return buffer[$ - l - 1 .. $ - 1];
+}
+
+// Converting an integer to string.
+@nogc nothrow pure @system unittest
+{
+    char[21] buf;
+
+    assert(integral2String(80, buf) == "80");
+    assert(integral2String(-80, buf) == "-80");
+    assert(integral2String(0, buf) == "0");
+    assert(integral2String(uint.max, buf) == "4294967295");
+    assert(integral2String(int.min, buf) == "-2147483648");
+}
+
+/*
+ * Double-double high-precision floating point number.
+ *
+ * The first element is a base value corresponding to the nearest approximation
+ * of the target $(D_PSYMBOL HP) value, and the second element is an offset
+ * value corresponding to the difference between the target value and the base.
+ * Thus, the $(D_PSYMBOL HP) value represented is the sum of the base and the
+ * offset.
+ */
+private struct HP
+{
+    private double base;
+    private double offset = 0.0;
+
+    private void normalize() @nogc nothrow pure @safe
+    {
+        const double target = this.base + this.offset;
+        this.offset -= target - this.base;
+        this.base = target;
+    }
+
+    private void multiply(ref const HP x, ref const HP y)
+    @nogc nothrow pure @safe
+    {
+        HP a, b;
+        long bt;
+
+        this.base = x.base * y.base;
+        copyFp(x.base, bt);
+        bt &= ulong.max << 27;
+        copyFp(bt, a.base);
+
+        a.offset = x.base - a.base;
+        copyFp(y.base, bt);
+        bt &= ulong.max << 27;
+        copyFp(bt, b.base);
+
+        b.offset = y.base - b.base;
+        this.offset = a.base * b.base - this.base
+                    + a.base * b.offset
+                    + a.offset * b.base
+                    + a.offset * b.offset;
+        this.offset += x.base * y.offset + x.offset * y.base;
+    }
+}
+
 private enum special = 0x7000;
 private enum char period = '.';
 
@@ -48,145 +175,121 @@ private static const ulong[20] powersOf10 = [
     10000000000000000000UL,
 ];
 
-private static const char[201] digitpair =
+private static const char[201] digitPairs =
     "0001020304050607080910111213141516171819202122232425262728293031323334353"
   ~ "6373839404142434445464748495051525354555657585960616263646566676869707172"
   ~ "737475767778798081828384858687888990919293949596979899";
 
-private static const double[23] bottom = [
-    1e+000, 1e+001, 1e+002, 1e+003, 1e+004, 1e+005, 1e+006, 1e+007, 1e+008,
-    1e+009, 1e+010, 1e+011, 1e+012, 1e+013, 1e+014, 1e+015, 1e+016, 1e+017,
-    1e+018, 1e+019, 1e+020, 1e+021, 1e+022,
-];
-
-private static const double[22] negativeBottom = [
-    1e-001, 1e-002, 1e-003, 1e-004, 1e-005, 1e-006, 1e-007, 1e-008, 1e-009,
-    1e-010, 1e-011, 1e-012, 1e-013, 1e-014, 1e-015, 1e-016, 1e-017, 1e-018,
-    1e-019, 1e-020, 1e-021, 1e-022,
-];
-
-private static const double[13] top = [
-    1e+023, 1e+046, 1e+069, 1e+092, 1e+115, 1e+138, 1e+161, 1e+184, 1e+207,
-    1e+230, 1e+253, 1e+276, 1e+299,
-];
-
-private static const double[13] negativeTop = [
-    1e-023, 1e-046, 1e-069, 1e-092, 1e-115, 1e-138, 1e-161, 1e-184, 1e-207,
-    1e-230, 1e-253, 1e-276, 1e-299,
+private static const HP[23] bottom = [
+    HP(1e+000), HP(1e+001), HP(1e+002), HP(1e+003), HP(1e+004), HP(1e+005),
+    HP(1e+006), HP(1e+007), HP(1e+008), HP(1e+009), HP(1e+010), HP(1e+011),
+    HP(1e+012), HP(1e+013), HP(1e+014), HP(1e+015), HP(1e+016), HP(1e+017),
+    HP(1e+018), HP(1e+019), HP(1e+020), HP(1e+021), HP(1e+022),
 ];
 
-private static const double[13] topError = [
-    8388608, 6.8601809640529717e+028, -7.253143638152921e+052,
-    -4.3377296974619174e+075, -1.5559416129466825e+098,
-    -3.2841562489204913e+121, -3.7745893248228135e+144,
-    -1.7356668416969134e+167, -3.8893577551088374e+190,
-    -9.9566444326005119e+213, 6.3641293062232429e+236,
-    -5.2069140800249813e+259, -5.2504760255204387e+282,
+private static const HP[22] negativeBottom = [
+    HP(1e-001, -5.551115123125783e-018),
+    HP(1e-002, -2.0816681711721684e-019),
+    HP(1e-003, -2.0816681711721686e-020),
+    HP(1e-004, -4.7921736023859299e-021),
+    HP(1e-005, -8.1803053914031305e-022),
+    HP(1e-006, 4.5251888174113741e-023),
+    HP(1e-007, 4.5251888174113739e-024),
+    HP(1e-008, -2.0922560830128471e-025),
+    HP(1e-009, -6.2281591457779853e-026),
+    HP(1e-010, -3.6432197315497743e-027),
+    HP(1e-011, 6.0503030718060191e-028),
+    HP(1e-012, 2.0113352370744385e-029),
+    HP(1e-013, -3.0373745563400371e-030),
+    HP(1e-014, 1.1806906454401013e-032),
+    HP(1e-015, -7.7705399876661076e-032),
+    HP(1e-016, 2.0902213275965398e-033),
+    HP(1e-017, -7.1542424054621921e-034),
+    HP(1e-018, -7.1542424054621926e-035),
+    HP(1e-019, 2.4754073164739869e-036),
+    HP(1e-020, 5.4846728545790429e-037),
+    HP(1e-021, 9.2462547772103625e-038),
+    HP(1e-022, -4.8596774326570872e-039),
 ];
 
-private static const double[22] negativeBottomError = [
-    -5.551115123125783e-018, -2.0816681711721684e-019,
-    -2.0816681711721686e-020, -4.7921736023859299e-021,
-    -8.1803053914031305e-022, 4.5251888174113741e-023,
-    4.5251888174113739e-024, -2.0922560830128471e-025,
-    -6.2281591457779853e-026, -3.6432197315497743e-027,
-    6.0503030718060191e-028, 2.0113352370744385e-029, -3.0373745563400371e-030,
-    1.1806906454401013e-032, -7.7705399876661076e-032, 2.0902213275965398e-033,
-    -7.1542424054621921e-034, -7.1542424054621926e-035,
-    2.4754073164739869e-036, 5.4846728545790429e-037, 9.2462547772103625e-038,
-    -4.8596774326570872e-039,
+private static const HP[13] top = [
+    HP(1e+023, 8388608),
+    HP(1e+046, 6.8601809640529717e+028),
+    HP(1e+069, -7.253143638152921e+052),
+    HP(1e+092, -4.3377296974619174e+075),
+    HP(1e+115, -1.5559416129466825e+098),
+    HP(1e+138, -3.2841562489204913e+121),
+    HP(1e+161, -3.7745893248228135e+144),
+    HP(1e+184, -1.7356668416969134e+167),
+    HP(1e+207, -3.8893577551088374e+190),
+    HP(1e+230, -9.9566444326005119e+213),
+    HP(1e+253, 6.3641293062232429e+236),
+    HP(1e+276, -5.2069140800249813e+259),
+    HP(1e+299, -5.2504760255204387e+282),
 ];
 
-private static const double[13] negativeTopError = [
-    3.9565301985100693e-040, -2.299904345391321e-063, 3.6506201437945798e-086,
-    1.1875228833981544e-109, -5.0644902316928607e-132,
-    -6.7156837247865426e-155, -2.812077463003139e-178,
-    -5.7778912386589953e-201, 7.4997100559334532e-224,
-    -4.6439668915134491e-247, -6.3691100762962136e-270,
-    -9.436808465446358e-293, // 8.0970921678014997e-317,
+private static const HP[13] negativeTop = [
+    HP(1e-023, 3.9565301985100693e-040L),
+    HP(1e-046, -2.299904345391321e-063L),
+    HP(1e-069, 3.6506201437945798e-086L),
+    HP(1e-092, 1.1875228833981544e-109L),
+    HP(1e-115, -5.0644902316928607e-132L),
+    HP(1e-138, -6.7156837247865426e-155L),
+    HP(1e-161, -2.812077463003139e-178L),
+    HP(1e-184, -5.7778912386589953e-201L),
+    HP(1e-207, 7.4997100559334532e-224L),
+    HP(1e-230, -4.6439668915134491e-247L),
+    HP(1e-253, -6.3691100762962136e-270L),
+    HP(1e-276, -9.436808465446358e-293L),
+    HP(1e-299, 8.0970921678014997e-317L),
 ];
 
 private enum ulong tenTo19th = 1000000000000000000UL;
 
-private void ddmultlo(A, B, C, D, E, F)(ref A oh,
-                                        ref B ol,
-                                        ref C xh,
-                                        ref D xl,
-                                        ref E yh,
-                                        ref F yl)
-{
-    ol = ol + (xh * yl + xl * yh);
-}
-
-private void ddmultlos(A, B, C, D)(ref A oh, ref B ol, ref C xh, ref D yl)
-{
-    ol = ol + (xh * yl);
-}
-
-private void ddrenorm(T, U)(ref T oh, ref U ol)
-{
-    double s;
-    s = oh + ol;
-    ol = ol - (s - oh);
-    oh = s;
-}
-
 // Power can be -323 to +350.
-private void raise2Power10(double* ohi,
-                           double* olo,
-                           double d,
-                           int power) @nogc nothrow pure
+private HP raise2Power10(const HP value, int power)
+@nogc nothrow pure @safe
 {
-    double ph, pl;
+    HP result;
     if ((power >= 0) && (power <= 22))
     {
-        ddmulthi(ph, pl, d, bottom[power]);
+        result.multiply(value, bottom[power]);
     }
     else
     {
-        int e, et, eb;
-        double p2h, p2l;
+        HP p2;
+        int e = power;
 
-        e = power;
         if (power < 0)
         {
             e = -e;
         }
-        et = (e * 0x2c9) >> 14; /* %23 */
+        int et = (e * 0x2c9) >> 14; // % 23
         if (et > 13)
         {
             et = 13;
         }
-        eb = e - (et * 23);
+        int eb = e - (et * 23);
 
-        ph = d;
-        pl = 0.0;
+        result = value;
         if (power < 0)
         {
-            if (eb)
+            if (eb != 0)
             {
                 --eb;
-                ddmulthi(ph, pl, d, negativeBottom[eb]);
-                ddmultlos(ph, pl, d, negativeBottomError[eb]);
+                result.multiply(value, negativeBottom[eb]);
             }
             if (et)
             {
-                ddrenorm(ph, pl);
+                result.normalize();
                 --et;
-                ddmulthi(p2h, p2l, ph, negativeTop[et]);
-                ddmultlo(p2h,
-                         p2l,
-                         ph,
-                         pl,
-                         negativeTop[et],
-                         negativeTopError[et]);
-                ph = p2h;
-                pl = p2l;
+                p2.multiply(result, negativeTop[et]);
+                result = p2;
             }
         }
         else
         {
-            if (eb)
+            if (eb != 0)
             {
                 e = eb;
                 if (eb > 22)
@@ -194,168 +297,141 @@ private void raise2Power10(double* ohi,
                     eb = 22;
                 }
                 e -= eb;
-                ddmulthi(ph, pl, d, bottom[eb]);
+                result.multiply(value, bottom[eb]);
                 if (e)
                 {
-                    ddrenorm(ph, pl);
-                    ddmulthi(p2h, p2l, ph, bottom[e]);
-                    ddmultlos(p2h, p2l, bottom[e], pl);
-                    ph = p2h;
-                    pl = p2l;
+                    result.normalize();
+                    p2.multiply(result, bottom[e]);
+                    result = p2;
                 }
             }
-            if (et)
+            if (et != 0)
             {
-                ddrenorm(ph, pl);
+                result.normalize();
                 --et;
-                ddmulthi(p2h, p2l, ph, top[et]);
-                ddmultlo(p2h, p2l, ph, pl, top[et], topError[et]);
-                ph = p2h;
-                pl = p2l;
+                p2.multiply(result, top[et]);
+                result = p2;
             }
         }
     }
-    ddrenorm(ph, pl);
-    *ohi = ph;
-    *olo = pl;
+    result.normalize();
+
+    return result;
 }
 
 /*
  * Given a float value, returns the significant bits in bits, and the position
- * of the decimal point in decimalPos. +/-Inf and NaN are specified by special
- * values returned in the decimalPos parameter.
- * fracDigits is absolute normally, but if you want from first significant
- * digits (got %g), or in 0x80000000
+ * of the decimal point in $(D_PARAM exponent). +/-Inf and NaN are specified
+ * by special values returned in the $(D_PARAM exponent). Sing bit is set in
+ * $(D_PARAM sign).
  */
-private int real2String(ref const(char)* start,
-                        ref uint len,
-                        char* out_,
-                        out int decimalPos,
-                        double value,
-                        uint fracDigits) @nogc nothrow pure
+private const(char)[] real2String(double value,
+                                  ref char[512] buffer,
+                                  out int exponent,
+                                  out bool sign) @nogc nothrow pure @trusted
 {
-    long bits = 0;
-    int e, tens;
-
-    double d = value;
-    copyFp(bits, d);
-    auto exponent = cast(int) ((bits >> 52) & 2047);
-    auto ng = cast(int) (bits >> 63);
-    if (ng)
+    long bits;
+    copyFp(value, bits);
+
+    exponent = (bits >> 52) & 0x7ff;
+    sign = signBit(value);
+    if (sign)
     {
-        d = -d;
+        value = -value;
     }
 
-    if (exponent == 2047) // Is NaN or inf?
+    if (exponent == 2047) // Is NaN or Inf?
     {
-        start = (bits & (((cast(ulong) 1) << 52) - 1)) ? "NaN" : "Inf";
-        decimalPos = special;
-        len = 3;
-        return ng;
+        exponent = special;
+        return (bits & ((1UL << 52) - 1)) != 0 ? "NaN" : "Inf";
     }
 
     if (exponent == 0) // Is zero or denormal?
     {
-        if ((bits << 1) == 0) // Do zero.
+        if ((bits << 1) == 0) // Zero.
         {
-            decimalPos = 1;
-            start = out_;
-            out_[0] = '0';
-            len = 1;
-            return ng;
+            exponent = 1;
+            buffer[0] = '0';
+            return buffer[0 .. 1];
         }
+
         // Find the right exponent for denormals.
+        for (long cursor = 1UL << 51; (bits & cursor) == 0; cursor >>= 1)
         {
-            long v = (cast(ulong) 1) << 51;
-            while ((bits & v) == 0)
-            {
-                --exponent;
-                v >>= 1;
-            }
+            --exponent;
         }
     }
 
-    // Find the decimal exponent as well as the decimal bits of the value.
+    // "617 / 2048" and "1233 / 4096" are estimations for the common logarithm
+    // (log10) of 2. Multiplied by a binary number it tells how big the number
+    // is in decimals, so it translates the binary exponent into decimal
+    // format. The estimation is tweaked to hit or undershoot by no more than
+    // 1 of log10 of all exponents 1..2046.
+    int tens = exponent - 1023; // Bias.
+    if (tens < 0)
     {
-        double ph, pl;
-
-        // log10 estimate - very specifically tweaked to hit or undershoot by
-        // no more than 1 of log10 of all exponents 1..2046.
-        tens = exponent - 1023;
-        if (tens < 0)
-        {
-            tens = (tens * 617) / 2048;
-        }
-        else
-        {
-            tens = ((tens * 1233) / 4096) + 1;
-        }
+        tens = tens * 617 / 2048;
+    }
+    else
+    {
+        tens = tens * 1233 / 4096 + 1;
+    }
 
-        // Move the significant bits into position and stick them into an int.
-        raise2Power10(&ph, &pl, d, 18 - tens);
+    // Move the significant bits into position and stick them into an int.
+    HP p = raise2Power10(HP(value), 18 - tens);
 
-        // Get full as much precision from double-double as possible.
-        bits = cast(long) ph;
-        double vh = cast(double) bits;
-        double ahi = (ph - vh);
-        double t = (ahi - ph);
-        double alo = (ph - (ahi - t)) - (vh + t);
-        bits += cast(long) (ahi + alo + pl);
+    // Get full as much precision from double-double as possible.
+    bits = cast(long) p.base;
+    double vh = cast(double) bits;
+    auto a = HP(p.base - vh);
+    double t = a.base - p.base;
+    a.offset = p.base - a.base + t - vh - t;
+    bits += cast(long) (a.base + a.offset + p.offset);
 
-        // Check if we undershot.
-        if ((cast(ulong) bits) >= tenTo19th)
-        {
-            ++tens;
-        }
+    // Check if we undershot (bits >= 10 ^ 19).
+    if ((cast(ulong) bits) >= 1000000000000000000UL)
+    {
+        ++tens;
     }
 
     // Now do the rounding in integer land.
-    if (fracDigits & 0x80000000)
-    {
-        fracDigits =  (fracDigits & 0x7ffffff) + 1;
-    }
-    else
+    enum uint fracDigits = 6;
+
+    uint dg = 1;
+    if ((cast(ulong) bits) >= powersOf10[9])
     {
-        fracDigits = tens + fracDigits;
+        dg = 10;
     }
-    if ((fracDigits < 24))
+    uint length;
+    while ((cast(ulong) bits) >= powersOf10[dg])
     {
-        uint dg = 1;
-        if (cast(ulong) bits >= powersOf10[9])
+        ++dg;
+        if (dg == 20)
         {
-            dg = 10;
+            goto NoRound;
         }
-        while (cast(ulong) bits >= powersOf10[dg])
+    }
+    if (fracDigits < dg)
+    {
+        // Add 0.5 at the right position and round.
+        length = dg - fracDigits;
+        if (length >= 24)
         {
-            ++dg;
-            if (dg == 20)
-            {
-                goto noround;
-            }
+            goto NoRound;
         }
-        if (fracDigits < dg)
+        ulong r = powersOf10[length];
+        bits = bits + (r / 2);
+        if ((cast(ulong) bits) >= powersOf10[dg])
         {
-            // Add 0.5 at the right position and round.
-            e = dg - fracDigits;
-            if (cast(uint) e >= 24)
-            {
-                goto noround;
-            }
-            ulong r = powersOf10[e];
-            bits = bits + (r / 2);
-            if (cast(ulong) bits >= powersOf10[dg])
-            {
-                ++tens;
-            }
-            bits /= r;
+            ++tens;
         }
-    noround:
+        bits /= r;
     }
+NoRound:
 
     // Kill long trailing runs of zeros.
     if (bits)
     {
-        uint n;
         for (;;)
         {
             if (bits <= 0xffffffff)
@@ -364,26 +440,26 @@ private int real2String(ref const(char)* start,
             }
             if (bits % 1000)
             {
-                goto donez;
+                goto Zeroed;
             }
             bits /= 1000;
         }
-        n = cast(uint) bits;
+        auto n = cast(uint) bits;
         while ((n % 1000) == 0)
         {
             n /= 1000;
         }
         bits = n;
-    donez:
     }
+Zeroed:
 
     // Convert to string.
-    out_ += 64;
-    e = 0;
-    for (;;)
+    auto result = buffer.ptr + 64;
+    length = 0;
+    while (true)
     {
         uint n;
-        char *o = out_ - 8;
+        char* o = result - 8;
         // Do the conversion in chunks of U32s (avoid most 64-bit divides,
         // worth it, constant denomiators be damned).
         if (bits >= 100000000)
@@ -398,35 +474,31 @@ private int real2String(ref const(char)* start,
         }
         while (n)
         {
-            out_ -= 2;
-            *cast(ushort*) out_ = *cast(ushort*) &digitpair[(n % 100) * 2];
+            result -= 2;
+            *cast(ushort*) result = *cast(ushort*) &digitPairs[(n % 100) * 2];
             n /= 100;
-            e += 2;
+            length += 2;
         }
         if (bits == 0)
         {
-            if ((e) && (out_[0] == '0'))
+            if ((length != 0) && (result[0] == '0'))
             {
-                ++out_;
-                --e;
+                ++result;
+                --length;
             }
             break;
         }
-        while (out_ != o)
+        for (; result !is o; ++length, --result)
         {
-            *--out_ = '0';
-            ++e;
+            *result = '0';
         }
     }
-
-    decimalPos = tens;
-    start = out_;
-    len = e;
-    return ng;
+    exponent = tens;
+    return result[0 .. length];
 }
 
 private void leadSign(bool negative, ref char[8] sign)
-@nogc nothrow pure
+@nogc nothrow pure @safe
 {
     sign[0] = 0;
     if (negative)
@@ -436,13 +508,13 @@ private void leadSign(bool negative, ref char[8] sign)
     }
 }
 
-// Copies d to bits w/ strict aliasing (this compiles to nothing on /Ox).
-private void copyFp(T, U)(ref T dest, ref U src)
+/*
+ * Copies double into long and back bitwise.
+ */
+private void copyFp(T, U)(ref const U src, ref T dest) @trusted
+if (T.sizeof == U.sizeof)
 {
-    for (int count = 0; count < 8; ++count)
-    {
-        (cast(char*) &dest)[count] = (cast(char*) &src)[count];
-    }
+    copy((&src)[0 .. 1], (&dest)[0 .. 1]);
 }
 
 private void ddmulthi(ref double oh,
@@ -453,13 +525,13 @@ private void ddmulthi(ref double oh,
     double ahi, bhi;
     long bt;
     oh = xh * yh;
-    copyFp(bt, xh);
+    copyFp(xh, bt);
     bt &= ((~cast(ulong) 0) << 27);
-    copyFp(ahi, bt);
+    copyFp(bt, ahi);
     double alo = xh - ahi;
-    copyFp(bt, yh);
+    copyFp(yh, bt);
     bt &= ((~cast(ulong) 0) << 27);
-    copyFp(bhi, bt);
+    copyFp(bt, bhi);
     double blo = yh - bhi;
     ol = ((ahi * bhi - oh) + ahi * blo + alo * bhi) + alo * blo;
 }
@@ -467,25 +539,6 @@ private void ddmulthi(ref double oh,
 package(tanya) String format(string fmt, Args...)(char[] buf, Args args)
 {
     String result;
-    char* bf = buf.ptr;
-
-    // Ok, we have a percent, read the modifiers first.
-    int precision = -1;
-    int tz = 0;
-    bool negative;
-
-    // Handle each replacement.
-    char[512] num; // Big enough for e308 (with commas) or e-307.
-    char[8] lead;
-    char[8] tail;
-    char *s;
-    uint l, n;
-    ulong n64;
-
-    double fv;
-
-    int decimalPos;
-    const(char)* sn;
 
     static if (isSomeString!(Args[0])) // String
     {
@@ -504,28 +557,23 @@ package(tanya) String format(string fmt, Args...)(char[] buf, Args args)
     }
     else static if (isFloatingPoint!(Args[0])) // Float
     {
-        fv = args[0];
-        if (precision == -1)
-        {
-            precision = 6;
-        }
-        else if (precision == 0)
-        {
-            precision = 1; // Default is 6.
-        }
+        char[512] num; // Big enough for e308 (with commas) or e-307.
+        char[8] lead;
+        char[8] tail = 0;
+        char *s;
+        int precision = 6;
+        int tz;
+        bool negative;
+        char* bf = buf.ptr;
+        int decimalPos;
+
         // Read the double into a string.
-        if (real2String(sn,
-                        l,
-                        num.ptr,
-                        decimalPos,
-                        fv,
-                        (precision - 1) | 0x80000000))
-        {
-            negative = true;
-        }
+        auto fv = real2String(args[0], num, decimalPos, negative);
+        const(char)* sn = fv.ptr;
+        auto l = cast(uint) fv.length;
 
         // Clamp the precision and delete extra zeros after clamp.
-        n = precision;
+        uint n = precision;
         if (l > cast(uint) precision)
         {
             l = precision;
@@ -570,7 +618,6 @@ package(tanya) String format(string fmt, Args...)(char[] buf, Args args)
         goto dofloatfromg;
 
     doexpfromg:
-        tail[0] = 0;
         leadSign(negative, lead);
         if (decimalPos == special)
         {
@@ -628,7 +675,6 @@ package(tanya) String format(string fmt, Args...)(char[] buf, Args args)
         goto flt_lead;
 
     dofloatfromg:
-        tail[0] = 0;
         leadSign(negative, lead);
         if (decimalPos == special)
         {
@@ -765,140 +811,67 @@ package(tanya) String format(string fmt, Args...)(char[] buf, Args args)
         // Get the length that we copied.
         l = cast(uint) (s - (num.ptr + 64));
         s = num.ptr + 64;
-    }
-    else static if (isPointer!(Args[0])) // Pointer
-    {
-        // Get the number.
-        n64 = cast(size_t) args[0];
-        size_t position = num.length;
 
-        do // Write at least "0" if the pointer is null.
+    scopy:
+        // Get fw=leading/trailing space, precision=leading zeros.
+        if (precision < cast(int) l)
         {
-            num[--position] = lowerHexDigits[cast(size_t) (n64 & 15)];
-            n64 >>= 4;
+            precision = l;
         }
-        while (n64 != 0);
+        n = precision + lead[0] + tail[0] + tz;
+        precision -= l;
 
-        result.insertBack("0x");
-        result.insertBack(num[position .. $]);
-    }
-    else static if (isIntegral!(Args[0])) // Integer
-    {
-        // Get the integer and abs it.
-        static if (Args[0].sizeof == 8)
+        // Copy the spaces and/or zeros.
+        if (precision)
         {
-            long k64 = args[0];
-            n64 = cast(ulong) k64;
-            static if (isSigned!(Args[0]))
+            int i;
+
+            // copy leader
+            sn = lead.ptr + 1;
+            while (lead[0])
             {
-                if (k64 < 0)
+                i = lead[0];
+                lead[0] -= cast(char) i;
+                while (i)
                 {
-                    n64 = cast(ulong) -k64;
-                    negative = true;
+                    *bf++ = *sn++;
+                    --i;
                 }
             }
-        }
-        else
-        {
-            int k = args[0];
-            n64 = cast(uint) k;
-            static if (isSigned!(Args[0]))
+
+            // Copy leading zeros.
+            while (precision > 0)
             {
-                if (k < 0)
+                i = precision;
+                precision -= i;
+                while (i)
                 {
-                    n64 = cast(uint) -k;
-                    negative = true;
+                    if (((cast(size_t) bf) & 3) == 0)
+                    {
+                        break;
+                    }
+                    *bf++ = '0';
+                    --i;
                 }
-            }
-        }
-
-        // Convert to string.
-        s = num.ptr + num.length;
-        l = 0;
-
-        for (;;)
-        {
-            // Do in 32-bit chunks (avoid lots of 64-bit divides even
-            // with constant denominators).
-            char *o = s - 8;
-            if (n64 >= 100000000)
-            {
-                n = cast(uint) (n64 % 100000000);
-                n64 /= 100000000;
-            }
-            else
-            {
-                n = cast(uint) n64;
-                n64 = 0;
-            }
-            while (n)
-            {
-                s -= 2;
-                *cast(ushort*) s = *cast(ushort*) &digitpair[(n % 100) * 2];
-                n /= 100;
-            }
-            while (n)
-            {
-                *--s = cast(char) (n % 10) + '0';
-                n /= 10;
-            }
-            if (n64 == 0)
-            {
-                if ((s[0] == '0') && (s != (num.ptr + num.length)))
+                while (i >= 4)
                 {
-                    ++s;
+                    *cast(uint*) bf = 0x30303030;
+                    bf += 4;
+                    i -= 4;
+                }
+                while (i)
+                {
+                    *bf++ = '0';
+                    --i;
                 }
-                break;
-            }
-            while (s != o)
-            {
-                *--s = '0';
             }
         }
 
-        tail[0] = 0;
-        leadSign(negative, lead);
-
-        // Get the length that we copied.
-        l = cast(uint) ((num.ptr + num.length) - s);
-        if (l == 0)
-        {
-            *--s = '0';
-            l = 1;
-        }
-        if (precision < 0)
-        {
-            precision = 0;
-        }
-    }
-    else
-    {
-        static assert(false);
-    }
-
-    if (result.length > 0)
-    {
-        return result;
-    }
-scopy:
-    // Get fw=leading/trailing space, precision=leading zeros.
-    if (precision < cast(int) l)
-    {
-        precision = l;
-    }
-    n = precision + lead[0] + tail[0] + tz;
-    precision -= l;
-
-    // Copy the spaces and/or zeros.
-    if (precision)
-    {
-        int i;
-
-        // copy leader
+        // copy leader if there is still one
         sn = lead.ptr + 1;
         while (lead[0])
         {
-            i = lead[0];
+            int i = lead[0];
             lead[0] -= cast(char) i;
             while (i)
             {
@@ -907,11 +880,25 @@ scopy:
             }
         }
 
-        // Copy leading zeros.
-        while (precision > 0)
+        // Copy the string.
+        n = l;
+        while (n)
         {
-            i = precision;
-            precision -= i;
+            int i = n;
+            n -= i;
+
+            while (i)
+            {
+                *bf++ = *s++;
+                --i;
+            }
+        }
+
+        // Copy trailing zeros.
+        while (tz)
+        {
+            int i = tz;
+            tz -= i;
             while (i)
             {
                 if (((cast(size_t) bf) & 3) == 0)
@@ -933,77 +920,49 @@ scopy:
                 --i;
             }
         }
-    }
 
-    // copy leader if there is still one
-    sn = lead.ptr + 1;
-    while (lead[0])
-    {
-        int i = lead[0];
-        lead[0] -= cast(char) i;
-        while (i)
+        // copy tail if there is one
+        sn = tail.ptr + 1;
+        while (tail[0])
         {
-            *bf++ = *sn++;
-            --i;
+            int i = tail[0];
+            tail[0] -= cast(char) i;
+            while (i)
+            {
+                *bf++ = *sn++;
+                --i;
+            }
         }
-    }
 
-    // Copy the string.
-    n = l;
-    while (n)
+        *bf = 0;
+        result = String(buf[0 .. cast(int) (bf - buf.ptr)]);
+    }
+    else static if (isPointer!(Args[0])) // Pointer
     {
-        int i = n;
-        n -= i;
+        char[size_t.sizeof * 2] buffer;
+        size_t position = buffer.length;
+        auto address = cast(size_t) args[0];
 
-        while (i)
+        do // Write at least "0" if the pointer is null.
         {
-            *bf++ = *s++;
-            --i;
+            buffer[--position] = lowerHexDigits[cast(size_t) (address & 15)];
+            address >>= 4;
         }
-    }
+        while (address != 0);
 
-    // Copy trailing zeros.
-    while (tz)
+        result.insertBack("0x");
+        result.insertBack(buffer[position .. $]);
+    }
+    else static if (isIntegral!(Args[0])) // Integer
     {
-        int i = tz;
-        tz -= i;
-        while (i)
-        {
-            if (((cast(size_t) bf) & 3) == 0)
-            {
-                break;
-            }
-            *bf++ = '0';
-            --i;
-        }
-        while (i >= 4)
-        {
-            *cast(uint*) bf = 0x30303030;
-            bf += 4;
-            i -= 4;
-        }
-        while (i)
-        {
-            *bf++ = '0';
-            --i;
-        }
+        char[21] buffer;
+        result.insertBack(integral2String(args[0], buffer));
     }
-
-    // copy tail if there is one
-    sn = tail.ptr + 1;
-    while (tail[0])
+    else
     {
-        int i = tail[0];
-        tail[0] -= cast(char) i;
-        while (i)
-        {
-            *bf++ = *sn++;
-            --i;
-        }
+        static assert(false);
     }
 
-    *bf = 0;
-    result = String(buf[0 .. cast(int) (bf - buf.ptr)]);
     return result;
 }