Bytearray() and structures for floating point values

smbunn — Wed, 17 Jan 2018 09:25:15 GMT

I found an answer. The function in Python by default packs the four bytes in little endian format. JavaScript expects big endian. By merely changing data = bytearray(struct.pack("f", vt)) to data = bytearray(struct.pack(">f", vt)) the unpack at the other end was simple. Java Script function decodeFloat(data1) { var binary = parseInt(data1, 16).toString(2); if (binary.length < 32) binary = ('00000000000000000000000000000000'+binary).substr(binary.length); var sign = (binary.charAt(0) == '1')?-1:1; var exponent = parseInt(binary.substr(1, 8), 2) - 127; var significandBase = binary.substr(9); var significandBin = '1'+significandBase; var i = 0; var val = 1; var significand = 0; if (exponent == -127) { if (significandBase.indexOf('1') == -1) return 0; else { exponent = -126; significandBin = '0'+significandBase; } } while (i < significandBin.length) { significand += val * parseInt(significandBin.charAt(i)); val = val / 2; i++; } return sign * significand * Math.pow(2, exponent); } // example use data = '408df220' // is floating point value 4.43580627441406255 value = decodeFloat(data); log.console('Value=', value); The code above is from https://stackoverflow.com/questions/4414077/read-write-bytes-of-float-in-js From a great website application at https://gregstoll.dyndns.org/~gregstoll/floattohex/ I produced the image below

bytearray, type and format confusion

jcaron — Tue, 31 Oct 2017 16:03:13 GMT

@soren Add ``` alone on the lines before and after your code, or prefix them all with 4 spaces to have them formatted as code. 40000 % 256 (or 40000 & 255, i.e. keeping the 8 least significant bits) = 64, which is the code point for @.

Topics tagged with bytearray

Bytearray() and structures for floating point values

bytearray, type and format confusion