314 lines
7.4 KiB
Go
314 lines
7.4 KiB
Go
// Copyright (c) 2012-2018 Ugorji Nwoke. All rights reserved.
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// Use of this source code is governed by a MIT license found in the LICENSE file.
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package codec
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import "strconv"
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// func parseFloat(b []byte, bitsize int) (f float64, err error) {
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// if bitsize == 32 {
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// return parseFloat32(b)
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// } else {
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// return parseFloat64(b)
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// }
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// }
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func parseFloat32(b []byte) (f float32, err error) {
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return parseFloat32_custom(b)
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// return parseFloat32_strconv(b)
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}
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func parseFloat64(b []byte) (f float64, err error) {
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return parseFloat64_custom(b)
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// return parseFloat64_strconv(b)
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}
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func parseFloat32_strconv(b []byte) (f float32, err error) {
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f64, err := strconv.ParseFloat(stringView(b), 32)
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f = float32(f64)
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return
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}
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func parseFloat64_strconv(b []byte) (f float64, err error) {
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return strconv.ParseFloat(stringView(b), 64)
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}
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// ------ parseFloat custom below --------
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// We assume that a lot of floating point numbers in json files will be
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// those that are handwritten, and with defined precision (in terms of number
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// of digits after decimal point), etc.
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//
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// We further assume that this ones can be written in exact format.
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//
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// strconv.ParseFloat has some unnecessary overhead which we can do without
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// for the common case:
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//
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// - expensive char-by-char check to see if underscores are in right place
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// - testing for and skipping underscores
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// - check if the string matches ignorecase +/- inf, +/- infinity, nan
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// - support for base 16 (0xFFFF...)
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//
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// The functions below will try a fast-path for floats which can be decoded
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// without any loss of precision, meaning they:
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//
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// - fits within the significand bits of the 32-bits or 64-bits
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// - exponent fits within the exponent value
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// - there is no truncation (any extra numbers are all trailing zeros)
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//
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// To figure out what the values are for maxMantDigits, use this idea below:
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//
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// 2^23 = 838 8608 (between 10^ 6 and 10^ 7) (significand bits of uint32)
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// 2^32 = 42 9496 7296 (between 10^ 9 and 10^10) (full uint32)
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// 2^52 = 4503 5996 2737 0496 (between 10^15 and 10^16) (significand bits of uint64)
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// 2^64 = 1844 6744 0737 0955 1616 (between 10^19 and 10^20) (full uint64)
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//
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// Since we only allow for up to what can comfortably fit into the significand
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// ignoring the exponent, and we only try to parse iff significand fits into the
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// Exact powers of 10.
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var float64pow10 = [...]float64{
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1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
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1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
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1e20, 1e21, 1e22,
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}
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var float32pow10 = [...]float32{1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10}
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type floatinfo struct {
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mantbits uint8
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expbits uint8
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bias int16
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exactPow10 int8 // Exact powers of ten are <= 10^N (32: 10, 64: 22)
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exactInts int8 // Exact integers are <= 10^N
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maxMantDigits int8 // 10^19 fits in uint64, while 10^9 fits in uint32
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}
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var fi32 = floatinfo{23, 8, -127, 10, 7, 9} // maxMantDigits = 9
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var fi64 = floatinfo{52, 11, -1023, 22, 15, 19} // maxMantDigits = 19
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const fMax64 = 1e15
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const fMax32 = 1e7
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const fBase = 10
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func parseFloatErr(b []byte) error {
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return &strconv.NumError{
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Func: "ParseFloat",
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Err: strconv.ErrSyntax,
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Num: string(b),
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}
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}
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func parseFloat32_custom(b []byte) (f float32, err error) {
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mantissa, exp, neg, trunc, bad, ok := readFloat(b, fi32)
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_ = trunc
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if bad {
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return 0, parseFloatErr(b)
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}
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if ok {
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// parseFloatDebug(b, 32, false, exp, trunc, ok)
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f = float32(mantissa)
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if neg {
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f = -f
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}
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if exp != 0 {
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indx := fExpIndx(exp)
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if exp < 0 { // int / 10^k
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f /= float32pow10[indx]
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} else { // exp > 0
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if exp > fi32.exactPow10 {
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f *= float32pow10[exp-fi32.exactPow10]
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if f < -fMax32 || f > fMax32 { // exponent too large - outside range
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goto FALLBACK
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}
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indx = uint8(fi32.exactPow10)
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}
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f *= float32pow10[indx]
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}
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}
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return
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}
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FALLBACK:
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// parseFloatDebug(b, 32, true, exp, trunc, ok)
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return parseFloat32_strconv(b)
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}
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func parseFloat64_custom(b []byte) (f float64, err error) {
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mantissa, exp, neg, trunc, bad, ok := readFloat(b, fi64)
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_ = trunc
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if bad {
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return 0, parseFloatErr(b)
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}
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if ok {
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f = float64(mantissa)
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if neg {
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f = -f
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}
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if exp != 0 {
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indx := fExpIndx(exp)
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if exp < 0 { // int / 10^k
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f /= float64pow10[indx]
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} else { // exp > 0
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if exp > fi64.exactPow10 {
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f *= float64pow10[exp-fi64.exactPow10]
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if f < -fMax64 || f > fMax64 { // exponent too large - outside range
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goto FALLBACK
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}
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indx = uint8(fi64.exactPow10)
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}
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f *= float64pow10[indx]
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}
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}
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return
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}
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FALLBACK:
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return parseFloat64_strconv(b)
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}
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func fExpIndx(v int8) uint8 {
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if v < 0 {
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return uint8(-v)
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}
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return uint8(v)
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}
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func readFloat(s []byte, y floatinfo) (mantissa uint64, exp int8, neg, trunc, bad, ok bool) {
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var i uint // make it uint, so that we eliminate bounds checking
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var slen = uint(len(s))
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if slen == 0 {
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bad = true
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return
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}
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switch s[0] {
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case '+':
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i++
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case '-':
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neg = true
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i++
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}
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// we considered punting early if string has length > maxMantDigits, but this doesn't account
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// for trailing 0's e.g. 700000000000000000000 can be encoded exactly as it is 7e20
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// var sawdot, sawdigits, sawexp bool
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var sawdot, sawexp bool
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var nd, ndMant, dp int8
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L:
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for ; i < slen; i++ {
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switch s[i] {
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case '.':
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if sawdot {
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bad = true
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return
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}
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sawdot = true
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dp = nd
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case '0':
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if nd == 0 { // ignore leading zeros
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dp--
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continue
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}
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nd++
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if ndMant < y.maxMantDigits {
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// mantissa = (mantissa << 1) + (mantissa << 3)
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mantissa *= fBase
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ndMant++
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}
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case '1', '2', '3', '4', '5', '6', '7', '8', '9':
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// sawdigits = true
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nd++
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if ndMant < y.maxMantDigits {
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// mantissa = (mantissa << 1) + (mantissa << 3) + uint64(s[i]-'0')
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mantissa = mantissa*fBase + uint64(s[i]-'0')
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// mantissa *= fBase
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// mantissa += uint64(s[i] - '0')
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ndMant++
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} else {
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trunc = true
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return // break L
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}
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case 'e', 'E':
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sawexp = true
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break L
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default:
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bad = true
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return
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}
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}
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// if !sawdigits {
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// bad = true
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// return
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// }
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if !sawdot {
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dp = nd
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}
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if sawexp {
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i++
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if i < slen {
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var eneg bool
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if s[i] == '+' {
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i++
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} else if s[i] == '-' {
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i++
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eneg = true
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}
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if i < slen {
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// for exact match, exponent is 1 or 2 digits (float64: -22 to 37, float32: -1 to 17).
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// exit quick if exponent is more than 2 digits.
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if i+2 < slen {
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return
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}
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var e int8
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if s[i] < '0' || s[i] > '9' {
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bad = true
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return
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}
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e = e*fBase + int8(s[i]-'0') // (e << 1) + (e << 3) + int8(s[i]-'0')
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i++
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if i < slen {
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if s[i] < '0' || s[i] > '9' {
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bad = true
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return
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}
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e = e*fBase + int8(s[i]-'0') // (e << 1) + (e << 3) + int8(s[i]-'0')
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i++
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}
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if eneg {
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dp -= e
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} else {
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dp += e
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}
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}
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}
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}
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if mantissa != 0 {
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if mantissa>>y.mantbits != 0 {
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return
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}
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exp = dp - ndMant
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if exp < -y.exactPow10 || exp > y.exactInts+y.exactPow10 { // cannot handle it
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return
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}
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}
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ok = true // && !trunc // if trunc=true, we return early (so here trunc=false)
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return
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}
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// fMul10ShiftU64
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// func parseFloatDebug(b []byte, bitsize int, strconv bool, exp int8, trunc, ok bool) {
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// if strconv {
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// xdebugf("parseFloat%d: delegating: %s, exp: %d, trunc: %v, ok: %v", bitsize, b, exp, trunc, ok)
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// } else {
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// xdebug2f("parseFloat%d: attempting: %s, exp: %d, trunc: %v, ok: %v", bitsize, b, exp, trunc, ok)
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// }
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// }
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