3 ms·

1+1=1? My maths education was a long time ago, but I triple checked with my calculator, and I'm uncertain this is quite right. My own mnemonic: SAXO. Shift, An

by tom_ 3y ago

1+1=1? My maths education was a long time ago, but I triple checked with my calculator, and I'm uncertain this is quite right. My own mnemonic: SAXO. Shift, And, Xor, Or. (Like a real Saxo, it's fun to go a bit faster like this, but you do have to trust everybody involved, because any accident is probably going to end up badly for you.) And now you know the bitwise precedence as well! And this ordering actually works out tidily for common operations: "x=a<<sa|b<<sb|c<<sb"; "x=p>>n&m"; "x=x&~ma|a<<sa"; and so on. You do need brackets sometimes, but fewer than you'd think, and it helps the unusual cases stand out. (Main annoying thing: a lot of compilers, even popular ones such as clang and gcc, don't actually seem to know what the precedence rules actually are, and generate warnings asking you to clarify. Presumably the authors didn't realise that C has an ISO standard, that can be consulted to answer this question? Very surprising.)

pcwalton 3y ago
> (Main annoying thing: a lot of compilers, even popular ones such as clang and gcc, don't actually seem to know what the precedence rules actually are, and generate warnings asking you to clarify. Presumably the authors didn't realise that C has an ISO standard, that can be consulted to answer this question? Very surprising.) The compilers do know what the precedence rules are, but they know that programmers don't routinely consult the ISO standard, so they emit those warnings to reduce the chance of error. Compilers are tools that are designed to help programmers avoid bugs. If they don't help programmers, they aren't doing their job.
- userbinator 3y ago
  Alternatively, they're encouraging programmers to be stupid and ignorant, causing a dumbing-down feedback loop which is ultimately damaging in the long term. It ain't no surprise if you see the crap that passes for software these days and the nosedive in quality, but that's a rant for some other time...
jovial_cavalier 3y ago
The analogy between logical AND and multiplication, and logical OR and addition is called Boolean Algebra, and it's very well known. The analogy is that when you set 1 to true and 0 to false, 1 becomes the identity for AND, and 0 becomes the identity for OR. Just as 1 is the identity for multiplication and 0 is the identity for addition. X * 0 = 0 | X ^ F = F X * 1 = X | X ^ T = X X + 0 = X | X V F = X X + 1 = ? | X V T = T <-- This one breaks the analogy With this, you can turn any logical expression into something that looks and feels like normal algebra, with the only weird exception being that both operators distribute over each other: A * (B + C) = A*B + A*C A + (B * C) = (A + B) * (A + C)
LordShredda 3y ago
1+1 isn't zero, so it's one.
- deleted 3y ago
  [deleted]
LeifCarrotson 3y ago
> 1+1=1? True + True = True, because "true" means "not zero" and "false" means "zero". In most all languages that permit int->bool casting, if(2) will evaluate to "true". The warnings clang and FCC generate are a style warning because it's unclear on casual reading. Even readers who know the precedence rules will typically want to insert the parentheses manually. If the meaning were undefined, the compiler would give an error, not a warning.
- hinkley 3y ago
  It’s true as long as you don’t chain more than a couple billion Boolean checks. More importantly, only if you don’t rely on short circuiting logic.
TylerE 3y ago
I suspect that most people here won’t get the joke. Renault pulled out of the US market 40 years ago, and was never more than a tiny player.
- tom_ 3y ago
  Better than that: the Saxo was from Citroen, who apparently haven't served North America since 1974 ;) The Renault equivalent would probably be the Clio. (Not a big hot hatch connoisseur though, I must admit - I just remember the Saxo in particular as having a reputation of hitting a bad spot on the tradeoff graph for flimsiness/power/good sense of average member of target demographic.)

by tom_ 3y ago

pcwalton 3y ago

> (Main annoying thing: a lot of compilers, even popular ones such as clang and gcc, don't actually seem to know what the precedence rules actually are, and generate warnings asking you to clarify. Presumably the authors didn't realise that C has an ISO standard, that can be consulted to answer this question? Very surprising.) The compilers do know what the precedence rules are, but they know that programmers don't routinely consult the ISO standard, so they emit those warnings to reduce the chance of error. Compilers are tools that are designed to help programmers avoid bugs. If they don't help programmers, they aren't doing their job.

userbinator 3y ago
Alternatively, they're encouraging programmers to be stupid and ignorant, causing a dumbing-down feedback loop which is ultimately damaging in the long term. It ain't no surprise if you see the crap that passes for software these days and the nosedive in quality, but that's a rant for some other time...

jovial_cavalier 3y ago

The analogy between logical AND and multiplication, and logical OR and addition is called Boolean Algebra, and it's very well known. The analogy is that when you set 1 to true and 0 to false, 1 becomes the identity for AND, and 0 becomes the identity for OR. Just as 1 is the identity for multiplication and 0 is the identity for addition. X * 0 = 0 | X ^ F = F X * 1 = X | X ^ T = X X + 0 = X | X V F = X X + 1 = ? | X V T = T <-- This one breaks the analogy With this, you can turn any logical expression into something that looks and feels like normal algebra, with the only weird exception being that both operators distribute over each other: A * (B + C) = A*B + A*C A + (B * C) = (A + B) * (A + C)

LordShredda 3y ago

1+1 isn't zero, so it's one.

deleted 3y ago
[deleted]

LeifCarrotson 3y ago

> 1+1=1? True + True = True, because "true" means "not zero" and "false" means "zero". In most all languages that permit int->bool casting, if(2) will evaluate to "true". The warnings clang and FCC generate are a style warning because it's unclear on casual reading. Even readers who know the precedence rules will typically want to insert the parentheses manually. If the meaning were undefined, the compiler would give an error, not a warning.

hinkley 3y ago
It’s true as long as you don’t chain more than a couple billion Boolean checks. More importantly, only if you don’t rely on short circuiting logic.

TylerE 3y ago

I suspect that most people here won’t get the joke. Renault pulled out of the US market 40 years ago, and was never more than a tiny player.

tom_ 3y ago
Better than that: the Saxo was from Citroen, who apparently haven't served North America since 1974 ;) The Renault equivalent would probably be the Clio. (Not a big hot hatch connoisseur though, I must admit - I just remember the Saxo in particular as having a reputation of hitting a bad spot on the tradeoff graph for flimsiness/power/good sense of average member of target demographic.)