@lemire/jstypes

jstypes

The jstypes library uses WebAssembly to support C-like arithmetic and logical operations in JavaScript. The essential strategy is to represent all numbers as string representing 64-bit hexadecimal numbers (we call them "hex64"). Conceptually these strings represent the content of a 64-bit register. These strings can be added, multiplied and so forth, resulting in other similar (hex64) strings. We can also convert these hex64 strings to other representations like 32-bit signed integers of 8-bit unsigned integers, as a processor would. Thus we use strings between "0000000000000000" and "FFFFFFFFFFFFFFFF" as inputs. Some instructions also expect a bit width parameter (out of 8, 16, 32, and 64). When specifying a bit width of 32, only the least significant 32 bits are processed. Thus we use strings between "0000000000000000" and "FFFFFFFFFFFFFFFF" as inputs. Some instructions also expect a bit width parameter (out of 8, 16, 32, and 64). When specifying a bit width of 32, only the least significant 32 bits are processed.

Example

The following JavaScript code

  console.log("FF000000000000 + 00111111111111 (32 bits) = "
   +jstypes.hex64_add("FF000000000000","00111111111111",32));

  console.log("FF000000000000 * 00111111111111 (64 bits) = "
  +jstypes.hex64_multiply("FF000000000000","00111111111111",64));

  console.log("FF000000000000 shifted by 35 bits in signed mode is = "
  +jstypes.hex64_shift_right_signed("FF00000000000000",35, 64));

should output...

FF000000000000 + 00111111111111 (32 bits) = 11111111
FF000000000000 * 00111111111111 (64 bits) = FFEF000000000000
FF000000000000 shifted by 35 bits in signed mode is = FFFFFFFFFFE00000

We support the following functions:

• hex64_add
• hex64_subtract
• hex64_multiply
• hex64_to_double
• hex64_to_float
• double_to_hex64
• hex64_to_signed
• unsigned_to_hex64
• signed_to_hex64
• float_to_hex64
• hex64_or
• hex64_and
• hex64_andnot
• hex64_xor
• hex64_equal
• hex64_lessthan_signed
• hex64_greaterthan_signed
• hex64_negate
• hex64_not
• hex64_shift_left
• hex64_shift_right_signed

Working node instructions

Go to a new directory and load the library:

npm init
npm i @lemire/jstypes

Create and run the following script (e.g., as test.js):

var jstypes = require("@lemire/jstypes")


jstypes.init().then(ready => {
  console.log("FF000000000000 + 00111111111111 (32 bits) = "
   +jstypes.hex64_add("FF000000000000","00111111111111",32));

  console.log("FF000000000000 * 00111111111111 (64 bits) = "
  +jstypes.hex64_multiply("FF000000000000","00111111111111",64));

  console.log("FF000000000000 shifted by 35 bits in signed mode is = "
  +jstypes.hex64_shift_right_signed("FF00000000000000",35, 64));

}).
catch(error => {
  console.log(error.message);
});

Todo and limitations

• This code is largely untested.
• It is unclear whether it works in a browser (only tested in node).
• We do not support floating-point operations (but it is easily added).
• It is unclear whether you can go from hex64 to float and back without error (you almost certainly can't).