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Diffstat (limited to 'vendor/github.com/pquerna/ffjson/fflib/v1/ftoa.go')
| -rw-r--r-- | vendor/github.com/pquerna/ffjson/fflib/v1/ftoa.go | 542 |
1 files changed, 542 insertions, 0 deletions
diff --git a/vendor/github.com/pquerna/ffjson/fflib/v1/ftoa.go b/vendor/github.com/pquerna/ffjson/fflib/v1/ftoa.go new file mode 100644 index 000000000..360d6dbcf --- /dev/null +++ b/vendor/github.com/pquerna/ffjson/fflib/v1/ftoa.go @@ -0,0 +1,542 @@ +package v1 + +/** + * Copyright 2015 Paul Querna, Klaus Post + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + * + */ + +/* Most of this file are on Go stdlib's strconv/ftoa.go */ +// Copyright 2009 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +import "math" + +// TODO: move elsewhere? +type floatInfo struct { + mantbits uint + expbits uint + bias int +} + +var optimize = true // can change for testing + +var float32info = floatInfo{23, 8, -127} +var float64info = floatInfo{52, 11, -1023} + +// AppendFloat appends the string form of the floating-point number f, +// as generated by FormatFloat +func AppendFloat(dst EncodingBuffer, val float64, fmt byte, prec, bitSize int) { + var bits uint64 + var flt *floatInfo + switch bitSize { + case 32: + bits = uint64(math.Float32bits(float32(val))) + flt = &float32info + case 64: + bits = math.Float64bits(val) + flt = &float64info + default: + panic("strconv: illegal AppendFloat/FormatFloat bitSize") + } + + neg := bits>>(flt.expbits+flt.mantbits) != 0 + exp := int(bits>>flt.mantbits) & (1<<flt.expbits - 1) + mant := bits & (uint64(1)<<flt.mantbits - 1) + + switch exp { + case 1<<flt.expbits - 1: + // Inf, NaN + var s string + switch { + case mant != 0: + s = "NaN" + case neg: + s = "-Inf" + default: + s = "+Inf" + } + dst.WriteString(s) + return + + case 0: + // denormalized + exp++ + + default: + // add implicit top bit + mant |= uint64(1) << flt.mantbits + } + exp += flt.bias + + // Pick off easy binary format. + if fmt == 'b' { + fmtB(dst, neg, mant, exp, flt) + return + } + + if !optimize { + bigFtoa(dst, prec, fmt, neg, mant, exp, flt) + return + } + + var digs decimalSlice + ok := false + // Negative precision means "only as much as needed to be exact." + shortest := prec < 0 + if shortest { + // Try Grisu3 algorithm. + f := new(extFloat) + lower, upper := f.AssignComputeBounds(mant, exp, neg, flt) + var buf [32]byte + digs.d = buf[:] + ok = f.ShortestDecimal(&digs, &lower, &upper) + if !ok { + bigFtoa(dst, prec, fmt, neg, mant, exp, flt) + return + } + // Precision for shortest representation mode. + switch fmt { + case 'e', 'E': + prec = max(digs.nd-1, 0) + case 'f': + prec = max(digs.nd-digs.dp, 0) + case 'g', 'G': + prec = digs.nd + } + } else if fmt != 'f' { + // Fixed number of digits. + digits := prec + switch fmt { + case 'e', 'E': + digits++ + case 'g', 'G': + if prec == 0 { + prec = 1 + } + digits = prec + } + if digits <= 15 { + // try fast algorithm when the number of digits is reasonable. + var buf [24]byte + digs.d = buf[:] + f := extFloat{mant, exp - int(flt.mantbits), neg} + ok = f.FixedDecimal(&digs, digits) + } + } + if !ok { + bigFtoa(dst, prec, fmt, neg, mant, exp, flt) + return + } + formatDigits(dst, shortest, neg, digs, prec, fmt) + return +} + +// bigFtoa uses multiprecision computations to format a float. +func bigFtoa(dst EncodingBuffer, prec int, fmt byte, neg bool, mant uint64, exp int, flt *floatInfo) { + d := new(decimal) + d.Assign(mant) + d.Shift(exp - int(flt.mantbits)) + var digs decimalSlice + shortest := prec < 0 + if shortest { + roundShortest(d, mant, exp, flt) + digs = decimalSlice{d: d.d[:], nd: d.nd, dp: d.dp} + // Precision for shortest representation mode. + switch fmt { + case 'e', 'E': + prec = digs.nd - 1 + case 'f': + prec = max(digs.nd-digs.dp, 0) + case 'g', 'G': + prec = digs.nd + } + } else { + // Round appropriately. + switch fmt { + case 'e', 'E': + d.Round(prec + 1) + case 'f': + d.Round(d.dp + prec) + case 'g', 'G': + if prec == 0 { + prec = 1 + } + d.Round(prec) + } + digs = decimalSlice{d: d.d[:], nd: d.nd, dp: d.dp} + } + formatDigits(dst, shortest, neg, digs, prec, fmt) + return +} + +func formatDigits(dst EncodingBuffer, shortest bool, neg bool, digs decimalSlice, prec int, fmt byte) { + switch fmt { + case 'e', 'E': + fmtE(dst, neg, digs, prec, fmt) + return + case 'f': + fmtF(dst, neg, digs, prec) + return + case 'g', 'G': + // trailing fractional zeros in 'e' form will be trimmed. + eprec := prec + if eprec > digs.nd && digs.nd >= digs.dp { + eprec = digs.nd + } + // %e is used if the exponent from the conversion + // is less than -4 or greater than or equal to the precision. + // if precision was the shortest possible, use precision 6 for this decision. + if shortest { + eprec = 6 + } + exp := digs.dp - 1 + if exp < -4 || exp >= eprec { + if prec > digs.nd { + prec = digs.nd + } + fmtE(dst, neg, digs, prec-1, fmt+'e'-'g') + return + } + if prec > digs.dp { + prec = digs.nd + } + fmtF(dst, neg, digs, max(prec-digs.dp, 0)) + return + } + + // unknown format + dst.Write([]byte{'%', fmt}) + return +} + +// Round d (= mant * 2^exp) to the shortest number of digits +// that will let the original floating point value be precisely +// reconstructed. Size is original floating point size (64 or 32). +func roundShortest(d *decimal, mant uint64, exp int, flt *floatInfo) { + // If mantissa is zero, the number is zero; stop now. + if mant == 0 { + d.nd = 0 + return + } + + // Compute upper and lower such that any decimal number + // between upper and lower (possibly inclusive) + // will round to the original floating point number. + + // We may see at once that the number is already shortest. + // + // Suppose d is not denormal, so that 2^exp <= d < 10^dp. + // The closest shorter number is at least 10^(dp-nd) away. + // The lower/upper bounds computed below are at distance + // at most 2^(exp-mantbits). + // + // So the number is already shortest if 10^(dp-nd) > 2^(exp-mantbits), + // or equivalently log2(10)*(dp-nd) > exp-mantbits. + // It is true if 332/100*(dp-nd) >= exp-mantbits (log2(10) > 3.32). + minexp := flt.bias + 1 // minimum possible exponent + if exp > minexp && 332*(d.dp-d.nd) >= 100*(exp-int(flt.mantbits)) { + // The number is already shortest. + return + } + + // d = mant << (exp - mantbits) + // Next highest floating point number is mant+1 << exp-mantbits. + // Our upper bound is halfway between, mant*2+1 << exp-mantbits-1. + upper := new(decimal) + upper.Assign(mant*2 + 1) + upper.Shift(exp - int(flt.mantbits) - 1) + + // d = mant << (exp - mantbits) + // Next lowest floating point number is mant-1 << exp-mantbits, + // unless mant-1 drops the significant bit and exp is not the minimum exp, + // in which case the next lowest is mant*2-1 << exp-mantbits-1. + // Either way, call it mantlo << explo-mantbits. + // Our lower bound is halfway between, mantlo*2+1 << explo-mantbits-1. + var mantlo uint64 + var explo int + if mant > 1<<flt.mantbits || exp == minexp { + mantlo = mant - 1 + explo = exp + } else { + mantlo = mant*2 - 1 + explo = exp - 1 + } + lower := new(decimal) + lower.Assign(mantlo*2 + 1) + lower.Shift(explo - int(flt.mantbits) - 1) + + // The upper and lower bounds are possible outputs only if + // the original mantissa is even, so that IEEE round-to-even + // would round to the original mantissa and not the neighbors. + inclusive := mant%2 == 0 + + // Now we can figure out the minimum number of digits required. + // Walk along until d has distinguished itself from upper and lower. + for i := 0; i < d.nd; i++ { + var l, m, u byte // lower, middle, upper digits + if i < lower.nd { + l = lower.d[i] + } else { + l = '0' + } + m = d.d[i] + if i < upper.nd { + u = upper.d[i] + } else { + u = '0' + } + + // Okay to round down (truncate) if lower has a different digit + // or if lower is inclusive and is exactly the result of rounding down. + okdown := l != m || (inclusive && l == m && i+1 == lower.nd) + + // Okay to round up if upper has a different digit and + // either upper is inclusive or upper is bigger than the result of rounding up. + okup := m != u && (inclusive || m+1 < u || i+1 < upper.nd) + + // If it's okay to do either, then round to the nearest one. + // If it's okay to do only one, do it. + switch { + case okdown && okup: + d.Round(i + 1) + return + case okdown: + d.RoundDown(i + 1) + return + case okup: + d.RoundUp(i + 1) + return + } + } +} + +type decimalSlice struct { + d []byte + nd, dp int + neg bool +} + +// %e: -d.ddddde±dd +func fmtE(dst EncodingBuffer, neg bool, d decimalSlice, prec int, fmt byte) { + // sign + if neg { + dst.WriteByte('-') + } + + // first digit + ch := byte('0') + if d.nd != 0 { + ch = d.d[0] + } + dst.WriteByte(ch) + + // .moredigits + if prec > 0 { + dst.WriteByte('.') + i := 1 + m := min(d.nd, prec+1) + if i < m { + dst.Write(d.d[i:m]) + i = m + } + for i <= prec { + dst.WriteByte('0') + i++ + } + } + + // e± + dst.WriteByte(fmt) + exp := d.dp - 1 + if d.nd == 0 { // special case: 0 has exponent 0 + exp = 0 + } + if exp < 0 { + ch = '-' + exp = -exp + } else { + ch = '+' + } + dst.WriteByte(ch) + + // dd or ddd + switch { + case exp < 10: + dst.WriteByte('0') + dst.WriteByte(byte(exp) + '0') + case exp < 100: + dst.WriteByte(byte(exp/10) + '0') + dst.WriteByte(byte(exp%10) + '0') + default: + dst.WriteByte(byte(exp/100) + '0') + dst.WriteByte(byte(exp/10)%10 + '0') + dst.WriteByte(byte(exp%10) + '0') + } + + return +} + +// %f: -ddddddd.ddddd +func fmtF(dst EncodingBuffer, neg bool, d decimalSlice, prec int) { + // sign + if neg { + dst.WriteByte('-') + } + + // integer, padded with zeros as needed. + if d.dp > 0 { + m := min(d.nd, d.dp) + dst.Write(d.d[:m]) + for ; m < d.dp; m++ { + dst.WriteByte('0') + } + } else { + dst.WriteByte('0') + } + + // fraction + if prec > 0 { + dst.WriteByte('.') + for i := 0; i < prec; i++ { + ch := byte('0') + if j := d.dp + i; 0 <= j && j < d.nd { + ch = d.d[j] + } + dst.WriteByte(ch) + } + } + + return +} + +// %b: -ddddddddp±ddd +func fmtB(dst EncodingBuffer, neg bool, mant uint64, exp int, flt *floatInfo) { + // sign + if neg { + dst.WriteByte('-') + } + + // mantissa + formatBits(dst, mant, 10, false) + + // p + dst.WriteByte('p') + + // ±exponent + exp -= int(flt.mantbits) + if exp >= 0 { + dst.WriteByte('+') + } + formatBits(dst, uint64(exp), 10, exp < 0) + + return +} + +func min(a, b int) int { + if a < b { + return a + } + return b +} + +func max(a, b int) int { + if a > b { + return a + } + return b +} + +// formatBits computes the string representation of u in the given base. +// If neg is set, u is treated as negative int64 value. +func formatBits(dst EncodingBuffer, u uint64, base int, neg bool) { + if base < 2 || base > len(digits) { + panic("strconv: illegal AppendInt/FormatInt base") + } + // 2 <= base && base <= len(digits) + + var a [64 + 1]byte // +1 for sign of 64bit value in base 2 + i := len(a) + + if neg { + u = -u + } + + // convert bits + if base == 10 { + // common case: use constants for / because + // the compiler can optimize it into a multiply+shift + + if ^uintptr(0)>>32 == 0 { + for u > uint64(^uintptr(0)) { + q := u / 1e9 + us := uintptr(u - q*1e9) // us % 1e9 fits into a uintptr + for j := 9; j > 0; j-- { + i-- + qs := us / 10 + a[i] = byte(us - qs*10 + '0') + us = qs + } + u = q + } + } + + // u guaranteed to fit into a uintptr + us := uintptr(u) + for us >= 10 { + i-- + q := us / 10 + a[i] = byte(us - q*10 + '0') + us = q + } + // u < 10 + i-- + a[i] = byte(us + '0') + + } else if s := shifts[base]; s > 0 { + // base is power of 2: use shifts and masks instead of / and % + b := uint64(base) + m := uintptr(b) - 1 // == 1<<s - 1 + for u >= b { + i-- + a[i] = digits[uintptr(u)&m] + u >>= s + } + // u < base + i-- + a[i] = digits[uintptr(u)] + + } else { + // general case + b := uint64(base) + for u >= b { + i-- + q := u / b + a[i] = digits[uintptr(u-q*b)] + u = q + } + // u < base + i-- + a[i] = digits[uintptr(u)] + } + + // add sign, if any + if neg { + i-- + a[i] = '-' + } + + dst.Write(a[i:]) +} |