std/private/dragonbox

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Copyright 2020 Junekey Jeon Copyright 2020 Alexander Bolz

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)

char* output_end = Dtoa(buffer, value);

Converts the given double-precision number into decimal form and stores the result in the given buffer.

The buffer must be large enough, i.e. >= DtoaMinBufferLength. The output format is similar to printf("%g"). The output is _not null-terminted.

The output is optimal, i.e. the output string

  1. rounds back to the input number when read in (using round-to-nearest-even)
  2. is as short as possible,
  3. is as close to the input number as possible.

Note: This function may temporarily write up to DtoaMinBufferLength characters into the buffer.

This file contains an implementation of Junekey Jeon's Dragonbox algorithm.

It is a simplified version of the reference implementation found here: https://github.com/jk-jeon/dragonbox

The reference implementation also works with single-precision floating-point numbers and has options to configure the rounding mode.

namespace Returns floor(x / 2^n).

Technically, right-shift of negative integers is implementation defined... Should easily be optimized into SAR (or equivalent) instruction.

Returns whether value is divisible by 2^e2Returns whether value is divisible by 5^e5Returns (x * y) / 2^128

Types

Double = object
  bits*: BitsType
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FloatingDecimal64 {.bycopy.} = object
  significand*: uint64
  exponent*: int32
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uint64x2 {.bycopy.} = object
  hi*: uint64
  lo*: uint64
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Consts

exponentBias: int32 = 1075'i32
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exponentMask: BitsType = 9218868437227405312'u64
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hiddenBit: BitsType = 4503599627370496'u64
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maxIeeeExponent: BitsType = 2047'u
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significandMask: BitsType = 4503599627370495'u64
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signMask: BitsType = 9223372036854775808'u64
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Procs

proc computeDelta(pow10: uint64x2; betaMinus1: int32): uint32 {.inline,
    ...raises: [], tags: [], forbids: [].}
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proc computePow10(k: int32): uint64x2 {.inline, ...raises: [], tags: [],
                                        forbids: [].}
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proc constructDouble(bits: BitsType): Double {....raises: [], tags: [], forbids: [].}
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proc constructDouble(value: ValueType): Double {....raises: [], tags: [],
    forbids: [].}
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proc decimalLength(v: uint64): int {.inline, ...raises: [], tags: [], forbids: [].}
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proc floorDivPow2(x: int32; n: int32): int32 {.inline, ...raises: [], tags: [],
    forbids: [].}
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proc floorLog2Pow10(e: int32): int32 {.inline, ...raises: [], tags: [], forbids: [].}
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proc floorLog10Pow2(e: int32): int32 {.inline, ...raises: [], tags: [], forbids: [].}
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proc floorLog10ThreeQuartersPow2(e: int32): int32 {.inline, ...raises: [],
    tags: [], forbids: [].}
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proc formatDigits[T: Ordinal](buffer: var openArray[char]; pos: T;
                              digits: uint64; decimalExponent: int;
                              forceTrailingDotZero = false): int {.inline.}
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proc hi32(x: uint64): uint32 {.inline, ...raises: [], tags: [], forbids: [].}
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proc isFinite(this: Double): bool {.noSideEffect, ...raises: [], tags: [],
                                    forbids: [].}
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proc isInf(this: Double): bool {.noSideEffect, ...raises: [], tags: [], forbids: [].}
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proc isIntegralEndpoint(twoF: uint64; e2: int32; minusK: int32): bool {.inline,
    ...raises: [], tags: [], forbids: [].}
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proc isIntegralMidpoint(twoF: uint64; e2: int32; minusK: int32): bool {.inline,
    ...raises: [], tags: [], forbids: [].}
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proc isNaN(this: Double): bool {.noSideEffect, ...raises: [], tags: [], forbids: [].}
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proc isZero(this: Double): bool {.noSideEffect, ...raises: [], tags: [],
                                  forbids: [].}
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proc lo32(x: uint64): uint32 {.inline, ...raises: [], tags: [], forbids: [].}
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proc mul128(a: uint64; b: uint64): uint64x2 {.inline, ...raises: [], tags: [],
    forbids: [].}
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proc mulParity(twoF: uint64; pow10: uint64x2; betaMinus1: int32): bool {.inline,
    ...raises: [], tags: [], forbids: [].}
1 mulx, 1 mul Source   Edit   
proc mulShift(x: uint64; y: uint64x2): uint64 {.inline, ...raises: [], tags: [],
    forbids: [].}
2 mulx Source   Edit   
proc multipleOfPow2(value: uint64; e2: int32): bool {.inline, ...raises: [],
    tags: [], forbids: [].}
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proc multipleOfPow5(value: uint64; e5: int32): bool {.inline, ...raises: [],
    tags: [], forbids: [].}
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proc physicalExponent(this: Double): BitsType {.noSideEffect, ...raises: [],
    tags: [], forbids: [].}
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proc physicalSignificand(this: Double): BitsType {.noSideEffect, ...raises: [],
    tags: [], forbids: [].}
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proc printDecimalDigitsBackwards(buf: var openArray[char]; pos: int;
                                 output64: uint64): int {.inline, ...raises: [],
    tags: [], forbids: [].}
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proc signBit(this: Double): int {.noSideEffect, ...raises: [], tags: [],
                                  forbids: [].}
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proc toChars(buffer: var openArray[char]; v: float; forceTrailingDotZero = false): int {.
    inline, ...raises: [], tags: [], forbids: [].}
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proc toDecimal64(ieeeSignificand: uint64; ieeeExponent: uint64): FloatingDecimal64 {.
    inline, ...raises: [], tags: [], forbids: [].}
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proc toDecimal64AsymmetricInterval(e2: int32): FloatingDecimal64 {.inline,
    ...raises: [], tags: [], forbids: [].}
NB: accept_lower_endpoint = true accept_upper_endpoint = true Source   Edit   
proc utoa8DigitsSkipTrailingZeros(buf: var openArray[char]; pos: int;
                                  digits: uint32): int {.inline, ...raises: [],
    tags: [], forbids: [].}
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