(42, all flavours) Integer Division - how?

[Albert Chan]

(12-13-2020 04:21 PM)Albert Chan Wrote:  Assuming q is correctly rounded (mode round-to-nearest), r = 0 or -1

This allowed optimization of my FMA (Fused-Multiply-Add) code.
Without using MOD, this is the fastest of all.

Bonus: it removed the integer arguments requirement.

PHP Code:

function idiv4(a,b)     -- asuumed b > 0
    local q = floor(a/b)
    local b1 = b * (0x1p27+1)
    local q1 = q * (0x1p27+1)
    b1 = b + b1 - b1    -- hi bits
    q1 = q + q1 - q1
    local b0 = b - b1   -- lo bits
    local q0 = q - q1
    if a - q1*b1 - q1*b0 - q0*b1 >= q0*b0 then return q end
    return q - 1
end 


It would be nice if Free42 exposed FMA(a,b,c) to the user ...