commit 80b5917fad7fb9d743ef78c0b4ac260511acaf6d (tree)
parent 648c1c5d28f3c3b1da1acf326b733c47436007d1
Author: Andrew Kelley <andrewrk@noreply.codeberg.org>
Date: Mon, 15 Dec 2025 01:05:50 +0100
Merge pull request 'Bigint improvements' (#30100) from unplanned/zig:bigint-improvements into master
Reviewed-on: https://codeberg.org/ziglang/zig/pulls/30100
Reviewed-by: jedisct1 <jedisct1@noreply.codeberg.org>
Diffstat:
2 files changed, 84 insertions(+), 43 deletions(-)
diff --git a/lib/std/math/big/int.zig b/lib/std/math/big/int.zig
@@ -17,6 +17,27 @@ const Endian = std.builtin.Endian;
const Signedness = std.builtin.Signedness;
const native_endian = builtin.cpu.arch.endian();
+// Comptime-computed constants for supported bases (2 - 36)
+// all values are set to 0 for bases 0 - 1, to make it possible to
+// access a constant for a given base b using `constants.value[b]`
+const Constants = struct {
+ // big_bases[b] is the biggest power of b that fit in a single Limb
+ // i.e. big_bases[b] = b^k < 2^@bitSizeOf(Limb) and b^(k+1) >= 2^@bitSizeOf(Limb)
+ big_bases: [37]Limb,
+ // digits_per_limb[b] is the value of k used in the previous field
+ digits_per_limb: [37]u8,
+};
+const constants: Constants = blk: {
+ @setEvalBranchQuota(2000);
+ var digits_per_limb = [_]u8{0} ** 37;
+ var bases = [_]Limb{0} ** 37;
+ for (2..37) |base| {
+ digits_per_limb[base] = @intCast(math.log(Limb, base, math.maxInt(Limb)));
+ bases[base] = std.math.pow(Limb, base, digits_per_limb[base]);
+ }
+ break :blk Constants{ .big_bases = bases, .digits_per_limb = digits_per_limb };
+};
+
/// Returns the number of limbs needed to store `scalar`, which must be a
/// primitive integer or float value.
/// Note: A comptime-known upper bound of this value that may be used
@@ -329,23 +350,15 @@ pub const Mutable = struct {
/// not allowed (e.g. 0x43 should simply be 43). Underscores in the input string are
/// ignored and can be used as digit separators.
///
- /// Asserts there is enough memory for the value in `self.limbs`. An upper bound on number of limbs can
+ /// There must be enough memory for the value in `self.limbs`. An upper bound on number of limbs can
/// be determined with `calcSetStringLimbCount`.
/// Asserts the base is in the range [2, 36].
///
/// Returns an error if the value has invalid digits for the requested base.
- ///
- /// `limbs_buffer` is used for temporary storage. The size required can be found with
- /// `calcSetStringLimbsBufferLen`.
- ///
- /// If `allocator` is provided, it will be used for temporary storage to improve
- /// multiplication performance. `error.OutOfMemory` is handled with a fallback algorithm.
pub fn setString(
self: *Mutable,
base: u8,
value: []const u8,
- limbs_buffer: []Limb,
- allocator: ?Allocator,
) error{InvalidCharacter}!void {
assert(base >= 2);
assert(base <= 36);
@@ -357,18 +370,41 @@ pub const Mutable = struct {
i += 1;
}
- const ap_base: Const = .{ .limbs = &[_]Limb{base}, .positive = true };
- self.set(0);
+ @memset(self.limbs, 0);
+ self.len = 1;
+ var limb: Limb = 0;
+ var j: usize = 0;
for (value[i..]) |ch| {
if (ch == '_') {
continue;
}
const d = try std.fmt.charToDigit(ch, base);
- const ap_d: Const = .{ .limbs = &[_]Limb{d}, .positive = true };
-
- self.mul(self.toConst(), ap_base, limbs_buffer, allocator);
- self.add(self.toConst(), ap_d);
+ limb *= base;
+ limb += d;
+ j += 1;
+
+ if (j == constants.digits_per_limb[base]) {
+ const len = @min(self.len + 1, self.limbs.len);
+ // r = a * b = a + a * (b - 1)
+ // we assert when self.limbs is not large enough to store the number
+ assert(!llmulLimb(.add, self.limbs[0..len], self.limbs[0..len], constants.big_bases[base] - 1));
+ assert(lladdcarry(self.limbs[0..len], self.limbs[0..len], &[1]Limb{limb}) == 0);
+
+ if (self.limbs.len > self.len and self.limbs[self.len] != 0)
+ self.len += 1;
+ j = 0;
+ limb = 0;
+ }
+ }
+ if (j > 0) {
+ const len = @min(self.len + 1, self.limbs.len);
+ // we assert when self.limbs is not large enough to store the number
+ assert(!llmulLimb(.add, self.limbs[0..len], self.limbs[0..len], math.pow(Limb, base, j) - 1));
+ assert(lladdcarry(self.limbs[0..len], self.limbs[0..len], &[1]Limb{limb}) == 0);
+
+ if (self.limbs.len > self.len and self.limbs[self.len] != 0)
+ self.len += 1;
}
self.positive = positive;
}
@@ -2081,7 +2117,7 @@ pub const Const = struct {
for (self.limbs[0..self.limbs.len]) |limb| {
std.debug.print("{x} ", .{limb});
}
- std.debug.print("len={} positive={}\n", .{ self.len, self.positive });
+ std.debug.print("len={} positive={}\n", .{ self.limbs.len, self.positive });
}
pub fn abs(self: Const) Const {
@@ -2884,10 +2920,8 @@ pub const Managed = struct {
pub fn setString(self: *Managed, base: u8, value: []const u8) !void {
if (base < 2 or base > 36) return error.InvalidBase;
try self.ensureCapacity(calcSetStringLimbCount(base, value.len));
- const limbs_buffer = try self.allocator.alloc(Limb, calcSetStringLimbsBufferLen(base, value.len));
- defer self.allocator.free(limbs_buffer);
var m = self.toMutable();
- try m.setString(base, value, limbs_buffer, self.allocator);
+ try m.setString(base, value);
self.setMetadata(m.positive, m.len);
}
@@ -3596,6 +3630,7 @@ fn llmulaccKaratsuba(
/// r = r (op) a.
/// The result is computed modulo `r.len`.
fn llaccum(comptime op: AccOp, r: []Limb, a: []const Limb) void {
+ assert(!slicesOverlap(r, a) or @intFromPtr(r.ptr) <= @intFromPtr(a.ptr));
if (op == .sub) {
_ = llsubcarry(r, r, a);
return;
@@ -3665,6 +3700,8 @@ fn llmulaccLong(comptime op: AccOp, r: []Limb, a: []const Limb, b: []const Limb)
/// The result is computed modulo `r.len`.
/// Returns whether the operation overflowed.
fn llmulLimb(comptime op: AccOp, acc: []Limb, y: []const Limb, xi: Limb) bool {
+ assert(!slicesOverlap(acc, y) or @intFromPtr(acc.ptr) <= @intFromPtr(y.ptr));
+
if (xi == 0) {
return false;
}
@@ -3727,6 +3764,8 @@ fn llsubcarry(r: []Limb, a: []const Limb, b: []const Limb) Limb {
assert(a.len != 0 and b.len != 0);
assert(a.len >= b.len);
assert(r.len >= a.len);
+ assert(!slicesOverlap(r, a) or @intFromPtr(r.ptr) <= @intFromPtr(a.ptr));
+ assert(!slicesOverlap(r, b) or @intFromPtr(r.ptr) <= @intFromPtr(b.ptr));
var i: usize = 0;
var borrow: Limb = 0;
@@ -3758,6 +3797,8 @@ fn lladdcarry(r: []Limb, a: []const Limb, b: []const Limb) Limb {
assert(a.len != 0 and b.len != 0);
assert(a.len >= b.len);
assert(r.len >= a.len);
+ assert(!slicesOverlap(r, a) or @intFromPtr(r.ptr) <= @intFromPtr(a.ptr));
+ assert(!slicesOverlap(r, b) or @intFromPtr(r.ptr) <= @intFromPtr(b.ptr));
var i: usize = 0;
var carry: Limb = 0;
diff --git a/lib/std/math/big/int_test.zig b/lib/std/math/big/int_test.zig
@@ -737,7 +737,7 @@ test "string to" {
defer testing.allocator.free(as);
const es = "120317241209124781241290847124";
- try testing.expect(mem.eql(u8, as, es));
+ try testing.expectEqualSlices(u8, es, as);
}
test "string to base base error" {
@@ -755,7 +755,7 @@ test "string to base 2" {
defer testing.allocator.free(as);
const es = "-1011";
- try testing.expect(mem.eql(u8, as, es));
+ try testing.expectEqualSlices(u8, es, as);
}
test "string to base 16" {
@@ -766,7 +766,7 @@ test "string to base 16" {
defer testing.allocator.free(as);
const es = "efffffff00000001eeeeeeefaaaaaaab";
- try testing.expect(mem.eql(u8, as, es));
+ try testing.expectEqualSlices(u8, es, as);
}
test "string to base 36" {
@@ -777,7 +777,7 @@ test "string to base 36" {
defer testing.allocator.free(as);
const es = "fifvthrv1mzt79ez9";
- try testing.expect(mem.eql(u8, as, es));
+ try testing.expectEqualSlices(u8, es, as);
}
test "neg string to" {
@@ -788,7 +788,7 @@ test "neg string to" {
defer testing.allocator.free(as);
const es = "-123907434";
- try testing.expect(mem.eql(u8, as, es));
+ try testing.expectEqualSlices(u8, es, as);
}
test "zero string to" {
@@ -799,7 +799,7 @@ test "zero string to" {
defer testing.allocator.free(as);
const es = "0";
- try testing.expect(mem.eql(u8, as, es));
+ try testing.expectEqualSlices(u8, es, as);
}
test "clone" {
@@ -3404,26 +3404,26 @@ test "big int conversion read twos complement with padding" {
var bit_count: usize = 12 * 8 + 1;
a.toConst().writeTwosComplement(buffer1[0..13], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0x1, 0xaa, 0xaa, 0xaa }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0x1, 0xaa, 0xaa, 0xaa }, buffer1);
a.toConst().writeTwosComplement(buffer1[0..13], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd, 0xaa, 0xaa, 0xaa }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd, 0xaa, 0xaa, 0xaa }, buffer1);
a.toConst().writeTwosComplement(buffer1[0..16], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0x1, 0x0, 0x0, 0x0 }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0x1, 0x0, 0x0, 0x0 }, buffer1);
a.toConst().writeTwosComplement(buffer1[0..16], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0x0, 0x0, 0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0x0, 0x0, 0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd }, buffer1);
@memset(buffer1, 0xaa);
try a.set(-0x01_02030405_06070809_0a0b0c0d);
bit_count = 12 * 8 + 2;
a.toConst().writeTwosComplement(buffer1[0..13], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xaa, 0xaa, 0xaa }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xaa, 0xaa, 0xaa }, buffer1);
a.toConst().writeTwosComplement(buffer1[0..13], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3, 0xaa, 0xaa, 0xaa }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3, 0xaa, 0xaa, 0xaa }, buffer1);
a.toConst().writeTwosComplement(buffer1[0..16], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff, 0xff, 0xff }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff, 0xff, 0xff }, buffer1);
a.toConst().writeTwosComplement(buffer1[0..16], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xff, 0xff, 0xff, 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3 }));
+ try testing.expectEqualSlices(u8, &[_]u8{ 0xff, 0xff, 0xff, 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3 }, buffer1);
}
test "big int write twos complement +/- zero" {
@@ -3438,13 +3438,13 @@ test "big int write twos complement +/- zero" {
// Test zero
m.toConst().writeTwosComplement(buffer1[0..13], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3)), buffer1);
m.toConst().writeTwosComplement(buffer1[0..13], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3)), buffer1);
m.toConst().writeTwosComplement(buffer1[0..16], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 16))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 16)), buffer1);
m.toConst().writeTwosComplement(buffer1[0..16], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 16))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 16)), buffer1);
@memset(buffer1, 0xaa);
m.positive = false;
@@ -3452,13 +3452,13 @@ test "big int write twos complement +/- zero" {
// Test negative zero
m.toConst().writeTwosComplement(buffer1[0..13], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3)), buffer1);
m.toConst().writeTwosComplement(buffer1[0..13], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 13) ++ ([_]u8{0xaa} ** 3)), buffer1);
m.toConst().writeTwosComplement(buffer1[0..16], .little);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 16))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 16)), buffer1);
m.toConst().writeTwosComplement(buffer1[0..16], .big);
- try testing.expect(std.mem.eql(u8, buffer1, &(([_]u8{0} ** 16))));
+ try testing.expectEqualSlices(u8, &(([_]u8{0} ** 16)), buffer1);
}
test "big int conversion write twos complement with padding" {
@@ -3816,7 +3816,7 @@ test "(BigInt) positive" {
const b_fmt = try std.fmt.allocPrint(testing.allocator, "{d}", .{b});
defer testing.allocator.free(b_fmt);
- try testing.expect(!mem.eql(u8, b_fmt, "(BigInt)"));
+ try testing.expect(!mem.eql(u8, "(BigInt)", b_fmt));
}
test "(BigInt) negative" {
@@ -3840,7 +3840,7 @@ test "(BigInt) negative" {
const b_fmt = try std.fmt.allocPrint(testing.allocator, "{d}", .{b});
defer testing.allocator.free(b_fmt);
- try testing.expect(mem.eql(u8, a_fmt, "(BigInt)"));
+ try testing.expectEqualSlices(u8, "(BigInt)", a_fmt);
try testing.expect(!mem.eql(u8, b_fmt, "(BigInt)"));
}
