print-float ( value -- string )
Ryū Float to String Conversion

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d2s ( value -- string )

Vocabulary
ryu

Inputs

value

a number

Outputs

string

a string

Word description
Convert the number into its shortest stable floating-point representation string using the Ryū algorithm.

Definition

USING: kernel math math.bitwise math.functions math.order
ryu.data ryu.private sequences.private ;

IN: ryu

:: print-float ( value -- string )
    value >float unpack-bits
    :> ( e2 m2 acceptBounds ieeeExponent<=1 sign output ) output 
    [
        m2 4 * :> mv mantissaBits 2^ m2 = not ieeeExponent<=1 or
        1 0 ?
        :> mmShift f f 0 0 0
        :> ( vmIsTrailingZeros! vrIsTrailingZeros! e10! vr! vm!
        ) e2 0 >= [
            e2 DOUBLE_LOG10_2_NUMERATOR *
            DOUBLE_LOG10_2_DENOMINATOR /i 0 max
            :> q q e10! q double-pow-5-bits
            DOUBLE_POW5_INV_BITCOUNT + 1 - :> k q k + e2 -
            :> i mmShift m2 q DOUBLE_POW5_INV_SPLIT nth-unsafe
            i mul-shift-all vr! swap vm! q 21 <= [
                mv 5 divisor? [
                    q mv multiple-of-power-of-5
                    vrIsTrailingZeros!
                ] [
                    acceptBounds [
                        q mv mmShift - 1 -
                        multiple-of-power-of-5
                        vmIsTrailingZeros!
                    ]
                    [ q mv 2 + multiple-of-power-of-5 1 0 ? - ]
                    if
                ] if
            ] when
        ] [
            e2 neg DOUBLE_LOG10_5_NUMERATOR *
            DOUBLE_LOG10_5_DENOMINATOR /i 1 [-] :> q q e2 +
            e10! e2 neg q -
            :> i i double-pow-5-bits DOUBLE_POW5_BITCOUNT -
            :> k q k -
            :> j mmShift m2 i DOUBLE_POW5_SPLIT nth-unsafe
            j mul-shift-all vr! swap vm! q 1 <= [
                mv 1 bitand bitnot q >=
                vrIsTrailingZeros! acceptBounds [
                    mv 1 - mmShift - bitnot 1 bitand q >=
                    vmIsTrailingZeros!
                ] [ 1 - ] if
            ] [
                q 63 < [
                    q 1 - on-bits mv bitand
                    zero? vrIsTrailingZeros!
                ] when
            ] if
        ] if [ decimal-length e10 + 1 - sign ] keep
        acceptBounds vmIsTrailingZeros vrIsTrailingZeros vr vm
        prepare-output produce-output
    ] unless* ;