Splinter-skills are super skills in one particular area. They show in the jagged skill/intelligence curve in autistic individuals at many levels.
I was hyperlexic too - ate a book in 3 hours, when I was 9.
Math - well - quite another matter
At 3-4 years, however, I could memorize a Mozart concerto and see it as a graphic score, while I sang along with the voices and I could shift between the voices via different intervals - according to the limits of my voice.
That was a little more advanced than usual.
The psychologist called it a savant trait, type "splinterskill". Not unusual in aspies.
In a few days its the birthday of Ludwig von Beethoven. He shoud be 250 years on next wednesday.
Beethoven (just like Mozart as Jensen write in his post) have also something special that people some discribe as a 'savant syndrome' At least, very special that keep composing after he did get deaf.