Messages in this thread | | | From | Miguel Ojeda <> | Date | Mon, 26 Apr 2021 20:01:21 +0200 | Subject | Re: [PATCH 00/13] [RFC] Rust support |
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On Mon, Apr 26, 2021 at 2:18 AM Linus Walleij <linus.walleij@linaro.org> wrote: > > static void yas53x_extract_calibration(u8 *data, struct yas5xx_calibration *c) > { > u64 val = get_unaligned_be64(data); > > c->a2 = FIELD_GET(GENMASK_ULL(63, 58), val) - 32; > c->a3 = FIELD_GET(GENMASK_ULL(57, 54), val) - 8; > c->a4 = FIELD_GET(GENMASK_ULL(53, 48), val) - 32; > c->a5 = FIELD_GET(GENMASK_ULL(47, 42), val) + 38; > c->a6 = FIELD_GET(GENMASK_ULL(41, 36), val) - 32; > c->a7 = FIELD_GET(GENMASK_ULL(35, 29), val) - 64; > c->a8 = FIELD_GET(GENMASK_ULL(28, 23), val) - 32; > c->a9 = FIELD_GET(GENMASK_ULL(22, 15), val); > c->k = FIELD_GET(GENMASK_ULL(14, 10), val) + 10; > c->dck = FIELD_GET(GENMASK_ULL(9, 7), val); > }
By the way, to give a more concrete example, this function could look like this:
fn yas53x_extract_calibration(data: [u8; 8], c: &mut yas5xx_calibration) { let val = u64::from_be_bytes(data);
c.a2 = FIELD_GET(GENMASK_ULL(63, 58), val) - 32; c.a3 = FIELD_GET(GENMASK_ULL(57, 54), val) - 8; c.a4 = FIELD_GET(GENMASK_ULL(53, 48), val) - 32; c.a5 = FIELD_GET(GENMASK_ULL(47, 42), val) + 38; c.a6 = FIELD_GET(GENMASK_ULL(41, 36), val) - 32; c.a7 = FIELD_GET(GENMASK_ULL(35, 29), val) - 64; c.a8 = FIELD_GET(GENMASK_ULL(28, 23), val) - 32; c.a9 = FIELD_GET(GENMASK_ULL(22, 15), val); c.k = FIELD_GET(GENMASK_ULL(14, 10), val) + 10; c.dck = FIELD_GET(GENMASK_ULL(9, 7), val) as u8; }
assuming `FIELD_GET()` returns `i32`. In particular, `GENMASK_ULL` and `FIELD_GET` can be written as normal functions, no need for macros (and can be `const fn` too -- i.e. can be evaluated at compile-time if needed).
As you see, it looks remarkably similar, and there is no `unsafe` because we pass the array of bytes instead of a raw pointer.
The caller needs to get the array from somewhere, of course -- if you only have a raw pointer to start with, then the caller will need an `unsafe` line to dereference it, as usual.
Cheers, Miguel
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