while loops question

[rancid bay]

you can use low for the current number, and the condition would be low <= high

eg. ||```rs
fn sum2(mut low: i32, high: i32) -> i32 {
let mut total = 0;

while low <= high {
    total += low;
    low += 1;
}
total

}```||

or just a for 😛

or you can do .sum() on a range and have no for or while

[chrome sleet]

why dont you just ((hi-lo)+1)*(hi+lo)/2

[rancid bay]

because they're learning

[chrome sleet]

¯_(ツ)_/¯

[rancid bay]

it's an adaptation of gauss' sum

which is a fast way to find the sum of all natural numbers up to n

that's ok

[chrome sleet]

my sum may be wrong

[rancid bay]

the optimizer can figure this particular optimization sometimes itself

[chrome sleet]

not here it cant

[rancid bay]

sometimes

[chrome sleet]

but the simple case it does

?godbolt ```rs
#[no_mangle]
pub fn gaussian_sum(to: usize) -> usize {
(0..to).sum()
}

[hybrid blade]

gaussian_sum:
        test    rdi, rdi
        je      .LBB0_1
        lea     rax, [rdi - 1]
        lea     rcx, [rdi - 2]
        mul     rcx
        shld    rdx, rax, 63
        lea     rax, [rdi + rdx]
        dec     rax
        ret
.LBB0_1:
        xor     eax, eax
        ret
```Note: only public functions (`pub fn`) are shown

[chrome sleet]

[rancid bay]

no loop

yay

but again, not that useful for a beginner

[chrome sleet]

?godbolt flags="-Copt-level=z" ```rs
#[no_mangle]
pub fn gaussian_sum(to: usize) -> usize {
(0..to).sum()
}

[hybrid blade]

core::iter::traits::iterator::Iterator::sum:
        jmp     qword ptr [rip + <usize as core::iter::traits::accum::Sum>::sum@GOTPCREL]

<usize as core::iter::traits::accum::Sum>::sum:
        cmp     rsi, rdi
        cmovbe  rsi, rdi
        mov     rax, rdi
        not     rax
        add     rax, rsi
        sub     rsi, rdi
        mul     rsi
        shrd    rax, rdx, 1
        imul    rsi, rdi
        add     rax, rsi
        ret

gaussian_sum:
        lea     rax, [rdi - 1]
        mul     rdi
        shrd    rax, rdx, 1
        ret
```Note: only public functions (`pub fn`) are shown

[chrome sleet]

xd