Last active
October 21, 2022 03:21
-
-
Save wjw12/12d43e578fb63208af898019b3d513f9 to your computer and use it in GitHub Desktop.
fp64_to_float
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| // input cannot be larger the 2^31 | |
| // this should allow at least 6 digits precision in the fractional part | |
| // https://stackoverflow.com/questions/45929493/node-js-maximum-safe-floating-point-number | |
| function fp64_to_float(a) { | |
| // avoid large number | |
| let mask = BigInt("0xffffffff000000000000000000000000") | |
| if ((a & mask) != 0n) { | |
| throw new Error("too large") | |
| } | |
| // integer part | |
| mask = BigInt("0x10000000000000000") | |
| let base = 1 | |
| let result = 0 | |
| for (let i = 0; i < 32; ++i) { | |
| if ((a & mask) != 0n) { result += base } | |
| base *= 2 | |
| mask = mask << 1n | |
| } | |
| // fractional part | |
| mask = BigInt("0x8000000000000000") | |
| base = 0.5 | |
| for (let i = 0; i < 32; ++i) { | |
| if ((a & mask) != 0n) { result += base } | |
| base /= 2 | |
| mask = mask >> 1n | |
| } | |
| console.log(result) | |
| } | |
| fp64_to_float(BigInt("9223372023969873920")) // 0.5 | |
| fp64_to_float(BigInt("36893488147419103232")) // 2.0 | |
| fp64_to_float(BigInt("25744505231652237576")) // 1.395612 | |
| fp64_to_float(BigInt("13217669704916664320")) // 0.716531 | |
| fp64_to_float(BigInt("1") << 95n) // 2147483648 | |
| fp64_to_float(BigInt("1") << 96n) // error |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment