31–40 of 109 posts
I'm wondering how you guys would optimize that code ? My naive approach would be something like this: const int numCountryIndicies = however many there are..; const char* countries = "A1\0A2\0..."; return (cc < numCountryIndicies)?countries[cc*2]:"UNKNOWN";
Run it on infinite multiverse, construct a mechanism to destroy the Universe every time branch predictor did not predict every single conditional correctly.
I'm wondering how you guys would optimize that code ? My naive approach would be something like this: const int numCountryIndicies = however many there are..; const char* countries = "A1\0A2\0..."; return (cc < numCountryIndicies)?countries[cc*2]:"UNKNOWN";
> I'm wondering how you guys would optimize that code ? Run it on infinite multiverse, construct a mechanism to destroy the Universe every time branch predictor did not predict every single conditional correctly.
This is a pretty amazing analysis that answers questions we probably all had as newbie programmers before realizing that code readability mattered more than efficiency 99.9% of the time.
More generally I don't think we should consider that readability and efficiency are at opposing ends of the same axis. With a bit of care and good tools it's often possible to get the best of both worlds, or close enough.
I'm wondering how you guys would optimize that code ? My naive approach would be something like this: const int numCountryIndicies = however many there are..; const char* countries = "A1\0A2\0..."; return (cc < numCountryIndicies)?countries[cc*2]:"UNKNOWN";
You have an off-by-one error. The strings are 3 bytes long. I'd write something similar, more or less; Probably the following, not for optimization, but more as a matter of style: const char countries[][3] = { "A1", "A0", // [...] }; // [...] int total_countries = (int) (sizeof(countries) / sizeof(countries[0])); return cc No need to hard code the length, and the cast is guaranteed to be within the bounds of an int o…
Stylistically-wise I think the best solution would be to write the array like:
const char countries[][3] = {
[0] = "A1",
[1] = "A0",
};
The “if (debug) log” example in the article is likely compiled to an always taken conditional jump past the logging call. And therefore not quite free. Nitpicking of course, I love such in-depth articles.
You can easily verify this in your specific code base but I believe the compiler prefers not-taken jumps for paths it predicts to be less frequently taken. You can provide hints that the path is a cold one to ensure the compiler uses the most efficient conditional branch layout. On some architectures the compiler will also provide this hint to the CPU (with a prefix, the instruction it selects, or a flag bit in the i…
Unrelated to the actual topic, but I believe there is a copy-paste bug in the first sample: const char *getCountry(int cc) { if(cc == 1) return "A1"; if(cc == 2) return "A2"; if(cc == 3) return "O1"; if(cc == 4) return "AD"; if(cc == 5) return "AE"; if(cc == 6) return "AF"; if(cc == 7) return "AG"; if(cc == 1) return "AI"; ... if(cc == 252) return "YT"; if(cc == 253) return "ZA"; if(cc == 254) return "ZM"; if(cc == 2…
Wouldn't the compiler optimize this to an array lookup? static const char* countries[257]; Or even: static const char countrycodes[514]; return countrycodes[i * 2];
static const char countrycodes[514];
return countrycodes[i * 2];
You know what another historical solution is called? Use a compile-time constant and let the damn optimizer optimize. (Virtually) no modern, widely used compiler would fail to optimize out `if (0) { ... }`.
Also, why does M1 performance matter to Cloudflare's software? I kinda doubt their servers are on Macbooks.
Earlier quoted context omitted.
You have an off-by-one error. The strings are 3 bytes long. I'd write something similar, more or less; Probably the following, not for optimization, but more as a matter of style: const char countries[][3] = { "A1", "A0", // [...] }; // [...] int total_countries = (int) (sizeof(countries) / sizeof(countries[0])); return cc No need to hard code the length, and the cast is guaranteed to be within the bounds of an int o…
I think that's the best solution (the only potential optimization I can think of would be to add a padding byte after every country to force 32bit alignment which would make the offset computation faster on some architectures, although probably not on x86). Stylistically-wise I think the best solution would be to write the array like: const char countries[][3] = { [0] = "A1", [1] = "A0", }; This way the codes are exp…
Good call. It might have caught the off-by-one mistake I made (the codes start from 1 and not 0 in the blog post). Maybe even switch to using an enum as our index instead of an int.