Speed up str(int)

[stuartarchibald]

As title.

Fixes #6189

[stuartarchibald]

Tested speed with:

from numba import njit
import time

@njit
def foo(n):
    c = 0
    for i in range(n):
        c += len(str(n))
    return c

def test(f):
    N = 10
    f(1)
    ts = time.time()
    for i in range(N):
        f(1000_000 + i)
    te = time.time()
    print("Elapsed = %s" % (te - ts))

test(foo.py_func)
test(foo)

This implementation seems at least twice as fast as cpython.

[esc]

I tried this locally and it does accelerate things quite a bit:

Before

 💣 zsh» python issue6202.py
Elapsed = 1.975172758102417
Elapsed = 20.156193017959595

After:

 💣 zsh» python issue6202.py
Elapsed = 2.0004079341888428
Elapsed = 0.9646546840667725

[stuartarchibald]

@esc is this ready to merge?

[esc]

@stuartarchibald it sure is! I have updated the label accordingly.