code wiki / _hdl_build / nx_div_pick_test.nx
`nx_div_pick_test.nx` source

1// nx_div_pick_test.nx -- proves the hardware-adaptive divider picker selects the
2// OPTIMAL divider per target, reproducing the honest crossover BY MEASUREMENT
3// (not hardcoded). The Seed's "grow to the hardware" mechanism, gated.
4//
5// From the proven honest latency race (nx_latency_metric_test):
6//   W=16:  r2=181  r4=139  Newton-shallow=166  Newton-deep=363  -> radix-4 optimal
7//   W=64:  r2=967  r4=743  Newton-shallow=320  Newton-deep=709  -> Newton optimal
8// So the picker must choose: W16 -> R4 (1) for BOTH multiplier models; W64 ->
9// NEWTON (2) for BOTH (shallow 320 and deep 709 both beat r4's 743). The sign-flip
10// R4->NEWTON across width IS the multiplicative-divider frontier, chosen optimally.
11//
12// Known answer (FAIL LOUD): "1 1 2 2" rc=0  (p16_shallow p16_deep p64_shallow p64_deep).
13
14import "nx_div_pick.nx"
15
16func _emit_num(v: i64) -> i64 {
17    let b: *u8 = sys_mmap(28); var n: i64 = v; if n < 0 { n = 0 - n }
18    let t2: *u8 = sys_mmap(28); var t: i64 = 0
19    if n == 0 { t2[0] = 48; t = 1 }
20    while n > 0 { t2[t] = 48 + (n % 10); n = n / 10; t = t + 1 }
21    var i: i64 = 0; while i < t { b[i] = t2[t - 1 - i]; i = i + 1 }
22    b[t] = 32; sys_write(1, b, t + 1); return 0
23}
24func _nl() -> i64 { let z: *u8 = sys_mmap(2); z[0] = 10; sys_write(1, z, 1); return 0 }
25
26func main() -> i64 {
27    let depth: *i64 = sys_mmap(8192 * 8) as *i64
28
29    let p16s: i64 = nx_div_pick(16, 0, depth)   // W=16, shallow (Wallace) multiplier
30    let p16d: i64 = nx_div_pick(16, 1, depth)   // W=16, deep (limb-schoolbook) multiplier
31    let p64s: i64 = nx_div_pick(64, 0, depth)   // W=64, shallow multiplier
32    let p64d: i64 = nx_div_pick(64, 1, depth)   // W=64, deep multiplier
33
34    _emit_num(p16s); _emit_num(p16d); _emit_num(p64s); _emit_num(p64d); _nl()
35
36    // Small width: radix-4 is optimal regardless of multiplier model (log W
37    // doesn't pay off). Large width: Newton/Goldschmidt is optimal for both.
38    if p16s != NXDP_R4     { sys_exit(1); return 1 }
39    if p16d != NXDP_R4     { sys_exit(2); return 2 }
40    if p64s != NXDP_NEWTON { sys_exit(3); return 3 }
41    if p64d != NXDP_NEWTON { sys_exit(4); return 4 }
42    sys_exit(0)
43    return 0
44}
nx_div_pick_test.nx source

`nx_div_pick_test.nx` source
