If your pack_number function builds the number up, the standard way to break it down is by extracting the least significant digit first using modulo and division. To get something that works well with SIMD we need a different approach. Instead of extracting the least significant digit from the bottom of an integer, we extract the most significant digit from the top of a fraction.

1. Convert to a fixed-point fraction: We scale our integer N into a fixed-point representation (e.g., using a 32-bit integer to represent the fraction). We do this by multiplying N by a precomputed reciprocal of 243.

2. Multiply by the base: Multiply the fraction by 3.

3. Extract: The integer portion of the result is your most significant trit.

4. Mask: Keep only the fractional remainder, and repeat.

The only operations here are multiplication, bitwise shift, and bitwise AND, i.e. perfectly suited for SIMD.

(in step 1 we replace the division with a multiplication by using the reciprocal. SIMD uses fixed-point integer arithmetic, not floating-point decimals)