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Add big int fits function (#1279)

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Returns whether the current value in an Int fits in the requested type.
This commit is contained in:
Marc Tiehuis 2018-07-23 02:11:27 +12:00 committed by Andrew Kelley
parent 07b6a3d335
commit d53fae3551
1 changed files with 39 additions and 0 deletions
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39
std/math/big/int.zig
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@ -150,6 +150,18 @@ pub const Int = struct {
return bits; return bits;
} }
pub fn fits(self: Int, comptime T: type) bool {
if (self.eqZero()) {
return true;
}
if (!T.is_signed and !self.positive) {
return false;
}
const req_bits = self.bitCountTwosComp() + @boolToInt(self.positive and T.is_signed);
return T.bit_count >= req_bits;
}
// Returns the approximate size of the integer in the given base. Negative values accomodate for // Returns the approximate size of the integer in the given base. Negative values accomodate for
// the minus sign. This is used for determining the number of characters needed to print the // the minus sign. This is used for determining the number of characters needed to print the
// value. It is inexact and will exceed the given value by 1-2 digits. // value. It is inexact and will exceed the given value by 1-2 digits.
@ -1217,6 +1229,33 @@ test "big.int bitcount/to" {
debug.assert((try a.to(i9)) == -129); debug.assert((try a.to(i9)) == -129);
} }
test "big.int fits" {
var a = try Int.init(al);
try a.set(0);
debug.assert(a.fits(u0));
debug.assert(a.fits(i0));
try a.set(255);
debug.assert(!a.fits(u0));
debug.assert(!a.fits(u1));
debug.assert(!a.fits(i8));
debug.assert(a.fits(u8));
debug.assert(a.fits(u9));
debug.assert(a.fits(i9));
try a.set(-128);
debug.assert(!a.fits(i7));
debug.assert(a.fits(i8));
debug.assert(a.fits(i9));
debug.assert(!a.fits(u9));
try a.set(0x1ffffffffeeeeeeee);
debug.assert(!a.fits(u32));
debug.assert(!a.fits(u64));
debug.assert(a.fits(u65));
}
test "big.int string set" { test "big.int string set" {
var a = try Int.init(al); var a = try Int.init(al);
try a.setString(10, "120317241209124781241290847124"); try a.setString(10, "120317241209124781241290847124");