md`# Float utils
> 计算公式 f(x) = tan(x) / scale, x 介于 [-127, 128] * unit, unit = PI / 256
需要实现：
- 转二进制形式：str toP8Bin(float)
- 二进制形式转单精度 float parseP8Bin(str)
`
toP8Bin = (function () {
let {atan, PI, round} = Math
const unit = PI / 255
// https://stackoverflow.com/questions/11433789/why-is-the-range-of-signed-byte-is-from-128-to-127-2s-complement-and-not-fro
const min = -128 * unit
return float => {
// [-Inf, Inf] -> [-PI/2, PI/2] -> [-128, 127] -> [0, 255]
let rad = atan(float * scale)
let uint = round((rad - min) / unit)
return intToBin(uint, 8)
}
})()
parseP8Bin = (function () {
const {tan, PI} = Math
const unit = PI / 255
return str => {
// [0, 255] -> [-128, 127] -> [-PI/2, PI/2] -> [-Inf, Inf]
let uint = parseInt(str, 2)
let int = uint - 128
return tan(unit * int) / scale
}
})()
toP8Bin(-1.5)
parseP8Bin('00001110')
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