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big ints: Some extra comments

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This commit is contained in:
Robin Voetter
2021-10-03 23:39:47 +02:00
parent ebcdfebaa6
commit b352564b36
1 changed files with 34 additions and 6 deletions
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40
lib/std/math/big/int.zig
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@@ -2158,15 +2158,27 @@ pub const Managed = struct {
r.setMetadata(m.positive, m.len);
}
/// r = a + b with 2s-complement wrapping semantics.
///
/// r, a and b may be aliases. If r aliases a or b, then caller must call
/// `r.ensureTwosCompCapacity` prior to calling `add`.
///
/// Returns an error if memory could not be allocated.
pub fn addWrap(r: *Managed, a: Const, b: Const, signedness: std.builtin.Signedness, bit_count: usize) Allocator.Error!void {
try r.ensureCapacity(calcTwosCompLimbCount(bit_count));
try r.ensureTwosCompCapacity(bit_count);
var m = r.toMutable();
m.addWrap(a, b, signedness, bit_count);
r.setMetadata(m.positive, m.len);
}
/// r = a + b with 2s-complement saturating semantics.
///
/// r, a and b may be aliases. If r aliases a or b, then caller must call
/// `r.ensureTwosCompCapacity` prior to calling `add`.
///
/// Returns an error if memory could not be allocated.
pub fn addSat(r: *Managed, a: Const, b: Const, signedness: std.builtin.Signedness, bit_count: usize) Allocator.Error!void {
try r.ensureCapacity(calcTwosCompLimbCount(bit_count));
try r.ensureTwosCompCapacity(bit_count);
var m = r.toMutable();
m.addSat(a, b, signedness, bit_count);
r.setMetadata(m.positive, m.len);
@@ -2184,15 +2196,27 @@ pub const Managed = struct {
r.setMetadata(m.positive, m.len);
}
/// r = a - b with 2s-complement wrapping semantics.
///
/// r, a and b may be aliases. If r aliases a or b, then caller must call
/// `r.ensureTwosCompCapacity` prior to calling `add`.
///
/// Returns an error if memory could not be allocated.
pub fn subWrap(r: *Managed, a: Const, b: Const, signedness: std.builtin.Signedness, bit_count: usize) Allocator.Error!void {
try r.ensureCapacity(calcTwosCompLimbCount(bit_count));
try r.ensureTwosCompCapacity(bit_count);
var m = r.toMutable();
m.subWrap(a, b, signedness, bit_count);
r.setMetadata(m.positive, m.len);
}
/// r = a - b with 2s-complement saturating semantics.
///
/// r, a and b may be aliases. If r aliases a or b, then caller must call
/// `r.ensureTwosCompCapacity` prior to calling `add`.
///
/// Returns an error if memory could not be allocated.
pub fn subSat(r: *Managed, a: Const, b: Const, signedness: std.builtin.Signedness, bit_count: usize) Allocator.Error!void {
try r.ensureCapacity(calcTwosCompLimbCount(bit_count));
try r.ensureTwosCompCapacity(bit_count);
var m = r.toMutable();
m.subSat(a, b, signedness, bit_count);
r.setMetadata(m.positive, m.len);
@@ -2229,7 +2253,7 @@ pub const Managed = struct {
/// rma = a * b with 2s-complement wrapping semantics.
///
/// rma, a and b may be aliases. However, it is more efficient if rma does not alias a or b.
/// If rma aliases a or b, then caller must call `rma.ensureCapacity(calcTwosCompLimbCount(bit_count))`
/// If rma aliases a or b, then caller must call `ensureTwosCompCapacity`
/// prior to calling `mul`.
///
/// Returns an error if memory could not be allocated.
@@ -2242,7 +2266,7 @@ pub const Managed = struct {
if (rma.limbs.ptr == b.limbs.ptr)
alias_count += 1;
try rma.ensureCapacity(calcTwosCompLimbCount(bit_count));
try rma.ensureTwosCompCapacity(bit_count);
var m = rma.toMutable();
if (alias_count == 0) {
m.mulWrapNoAlias(a, b, signedness, bit_count, rma.allocator);
@@ -2255,6 +2279,10 @@ pub const Managed = struct {
rma.setMetadata(m.positive, m.len);
}
pub fn ensureTwosCompCapacity(r: *Managed, bit_count: usize) !void {
try r.ensureCapacity(calcTwosCompLimbCount(bit_count));
}
pub fn ensureAddScalarCapacity(r: *Managed, a: Const, scalar: anytype) !void {
try r.ensureCapacity(math.max(a.limbs.len, calcLimbLen(scalar)) + 1);
}