vaxdata is an implementation of libvaxdata in Go. vaxdata allows conversions to and from VAX floating point formats. The following conversions are supported:
- VAX F_Float to and from
float32 - VAX G_Float to and from
float64
import "github.com/sixlettervariables/vaxdata"
var (
f float32
g float64
)
f, err := Float32fromVaxFFloat([]byte { 0x00, 0x00, 0x40, 0x80 })
// f == 1.0
g, err := Float64fromVaxGFloat([]byte{0x2D, 0x18, 0x54, 0x44, 0x21, 0xFB, 0x40, 0x29 })
// g == 3.141592653589793func Float32fromVaxFFloat(buf []byte) (float32, error)Float32fromVaxFFloat returns the float32 representation of a VAX F_Float.
func Float64fromVaxGFloat(buf []byte) (float64, error)Float64fromVaxGFloat returns the float64 representation of a VAX G_Float.
func WriteFFloat(w io.Writer, f float32) errorWriteFFloat takes a float32 and writes an F_Float to the io.Writer.
func WriteGFloat(w io.Writer, f float64) errorWriteGFloat takes a float64 and writes an G_Float to the io.Writer.
type VaxFFloat uint32VaxFFloat represents a VAX F_Float 32-bit value
func VaxFFloatfromFloat32(f float32) (VaxFFloat, error)VaxFFloatfromFloat32 returns the VAX F_Float representation of a float32.
type VaxFFloatReader struct {
}VaxFFloatReader reads float32 values from F_Float's in the underlying io.Reader.
func NewVaxFFloatReader(r io.Reader) *VaxFFloatReaderNewVaxFFloatReader creates a new VaxFFloatReader. VaxFFloatReader.Read reads a float32 from a F_Float in the underlying io.Reader.
func (vaxin *VaxFFloatReader) Read() (float32, error)Read takes a F_Float from the underlying io.Reader and returns a float32.
type VaxGFloat uint64VaxGFloat represents a VAX G_Float 64-bit value
func VaxGFloatfromFloat64(f float64) (VaxGFloat, error)VaxGFloatfromFloat64 returns the VAX G_Float representation of a float64.
type VaxGFloatReader struct {
}VaxGFloatReader reads float64 values from G_Float's in the underlying io.Reader.
func NewVaxGFloatReader(r io.Reader) *VaxGFloatReaderNewVaxGFloatReader creates a new VaxGFloatReader. VaxGFloatReader.Read reads a float64 from a G_Float in the underlying io.Reader.
func (vaxin *VaxGFloatReader) Read() (float64, error)Read takes a G_Float from the underlying io.Reader and returns a float64
// Floating point data format invariants
const (
SignBit uint32 = 0x80000000
VaxFExponentMask uint32 = 0x7F800000
VaxFExponentSize uint32 = 8
VaxFExponentBias uint32 = (1 << (VaxFExponentSize - 1))
VaxFMantissaMask uint32 = 0x007FFFFF
VaxFMantissaSize uint32 = 23
VaxFHiddenBit uint32 = (1 << VaxFMantissaSize)
VaxGExponentMask uint32 = 0x7FF00000
VaxGExponentSize uint32 = 11
VaxGExponentBias uint32 = (1 << (VaxGExponentSize - 1))
VaxGMantissaMask uint32 = 0x000FFFFF
VaxGMantissaSize uint32 = 20
VaxGHiddenBit uint32 = (1 << VaxGMantissaSize)
IeeeSExponentMask uint32 = 0x7F800000
IeeeSExponentSize uint32 = 8
IeeeSExponentBias uint32 = ((1 << (IeeeSExponentSize - 1)) - 1)
IeeeSMantissaMask uint32 = 0x007FFFFF
IeeeSMantissaSize uint32 = 23
IeeeSHiddenBit uint32 = (1 << IeeeSMantissaSize)
IeeeTExponentMask uint32 = 0x7FF00000
IeeeTExponentSize uint32 = 11
IeeeTExponentBias uint32 = ((1 << (IeeeTExponentSize - 1)) - 1)
IeeeTMantissaMask uint32 = 0x000FFFFF
IeeeTMantissaSize uint32 = 20
IeeeTHiddenBit uint32 = (1 << IeeeTMantissaSize)
)Reproduced from convert_vax_data.h.
Most Unix machines implement the ANSI/IEEE 754-1985 floating-point arithmetic standard. VAX and IEEE formats are similar (after byte-swapping). The high-order bit is a sign bit (s). This is followed by a biased exponent (e), and a (usually) hidden-bit normalized mantissa (m). They differ in the number used to bias the exponent, the location of the implicit binary point for the mantissa, and the representation of exceptional numbers (e.g., +/-infinity).
VAX floating-point formats: (-1)^s * 2^(e-bias) * 0.1m
31 15 0
| | |
F_floating mmmmmmmmmmmmmmmmseeeeeeeemmmmmmm bias = 128
D_floating mmmmmmmmmmmmmmmmseeeeeeeemmmmmmm bias = 128
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
G_floating mmmmmmmmmmmmmmmmseeeeeeeeeeemmmm bias = 1024
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
H_floating mmmmmmmmmmmmmmmmseeeeeeeeeeeeeee bias = 16384
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
IEEE floating-point formats: (-1)^s * 2^(e-bias) * 1.m
31 15 0
| | |
S_floating seeeeeeeemmmmmmmmmmmmmmmmmmmmmmm bias = 127
T_floating seeeeeeeeeeemmmmmmmmmmmmmmmmmmmm bias = 1023
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
X_floating seeeeeeeeeeeeeeemmmmmmmmmmmmmmmm bias = 16383
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
A VAX floating-point number is converted to IEEE floating-point format by subtracting (1+VAX_bias-IEEE_bias) from the exponent field to (1) adjust from VAX 0.1m hidden-bit normalization to IEEE 1.m hidden-bit normalization and (2) adjust the bias from VAX format to IEEE format. True zero [s=e=m=0] and dirty zero [s=e=0, m<>0] are special cases which must be recognized and handled separately. Both VAX zeros are converted to IEEE +zero [s=e=m=0].
Numbers whose absolute value is too small to represent in the normalized IEEE format illustrated above are converted to subnormal form [e=0, m>0]: (-1)^s * 2^(1-bias) * 0.m. Numbers whose absolute value is too small to represent in subnormal form are set to 0.0 (silent underflow).
Note: If the fractional part of the VAX floating-point number is too large for the corresponding IEEE floating-point format, bits are simply discarded from the right. Thus, the remaining fractional part is chopped, not rounded to the lowest-order bit. This can only occur when the conversion requires IEEE subnormal form.
A VAX floating-point reserved operand [s=1, e=0, m=any] causes a SIGFPE exception to be raised. The converted result is set to zero.
Conversely, an IEEE floating-point number is converted to VAX floating-point format by adding (1+VAX_bias-IEEE_bias) to the exponent field. +zero [s=e=m=0], -zero [s=1, e=m=0], infinities [s=X, e=all-1's, m=0], and NaNs [s=X, e=all-1's, m<>0] are special cases which must be recognized and handled separately. Both IEEE zeros are converted to VAX true zero [s=e=m=0]. Infinities and NaNs cause a SIGFPE exception to be raised. The result returned has the largest VAX exponent [e=all-1's] and zero mantissa [m=0] with the same sign as the original.
Numbers whose absolute value is too small to represent in the normalized VAX format illustrated above are set to 0.0 (silent underflow). (VAX floating-point format does not support subnormal numbers.) Numbers whose absolute value exceeds the largest representable VAX-format number cause a SIGFPE exception to be raised (overflow). (VAX floating-point format does not have reserved bit patterns for infinities and not-a-numbers [NaNs].) The result returned has the largest VAX exponent and mantissa [e=m= all-1's] with the same sign as the original.
All contributions to the project will be considered for inclusion, simply submit a pull request!
- Fork the repository (read more detailed steps).
- Create a branch
- Make and commit your changes
- Push your changes back to your fork.
- Submit a pull request (read more detailed steps).
The MIT License
Portions copyright (C) 2016 Christopher A. Watford, no claims made to original USGS work in public domain.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice, this permission notice, and the disclaimer below shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
Original libvaxdata Disclaimer
Although this program has been used by the USGS, no warranty, expressed or implied, is made by the USGS or the United States Government as to the accuracy and functioning of the program and related program material, nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith.