mirror of
https://github.com/roc-lang/roc.git
synced 2025-09-28 14:24:45 +00:00
233 lines
6.4 KiB
Zig
233 lines
6.4 KiB
Zig
const std = @import("std");
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const math = std.math;
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pub const RocDec = struct {
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num: i128,
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pub const decimal_places: u32 = 18;
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pub const min: RocDec = .{ .num = math.minInt(i128) };
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pub const max: RocDec = .{ .num = math.maxInt(i128) };
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pub const one_point_zero: RocDec = .{ .num = comptime math.pow(i128, 10, RocDec.decimal_places) };
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pub fn add(self: RocDec, other: RocDec) RocDec {
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var answer: i128 = undefined;
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const overflowed = @addWithOverflow(i128, self.num, other.num, &answer);
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if (!overflowed) {
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return RocDec{ .num = answer };
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} else {
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std.debug.panic("TODO runtime exception for overflow!", .{});
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}
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}
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pub fn mul(self: RocDec, other: RocDec) RocDec {
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const self_i128 = self.num;
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const other_i128 = other.num;
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// const answer = 0; //self_i256 * other_i256;
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const is_answer_negative = (self_i128 < 0) != (other_i128 < 0);
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const self_u128 = @intCast(u128, math.absInt(self_i128) catch {
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if (other_i128 == 0) {
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return .{ .num = 0 };
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} else if (other_i128 == RocDec.one_point_zero.num) {
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return self;
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} else {
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std.debug.panic("TODO runtime exception for overflow!", .{});
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}
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});
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const other_u128 = @intCast(u128, math.absInt(other_i128) catch {
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if (self_i128 == 0) {
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return .{ .num = 0 };
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} else if (self_i128 == RocDec.one_point_zero.num) {
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return other;
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} else {
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std.debug.panic("TODO runtime exception for overflow!", .{});
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}
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});
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const unsigned_answer: i128 = mul_and_decimalize(self_u128, other_u128);
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if (is_answer_negative) {
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return .{ .num = -unsigned_answer };
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} else {
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return .{ .num = unsigned_answer };
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}
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}
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};
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const U256 = struct {
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hi: u128,
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lo: u128,
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};
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fn mul_and_decimalize(a: u128, b: u128) i128 {
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const answer_u256 = mul_u128(a, b);
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var lhs_hi = answer_u256.hi;
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var lhs_lo = answer_u256.lo;
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// Divide - or just add 1, multiply by floor(2^315/10^18), then right shift 315 times.
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// floor(2^315/10^18) is 66749594872528440074844428317798503581334516323645399060845050244444366430645
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// Add 1.
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// This can't overflow because the intial numbers are only 127bit due to removing the sign bit.
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var overflowed = @addWithOverflow(u128, lhs_lo, 1, &lhs_lo);
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lhs_hi = blk: {
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if (overflowed) {
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break :blk lhs_hi + 1;
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} else {
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break :blk lhs_hi + 0;
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}
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};
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// This needs to do multiplication in a way that expands,
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// since we throw away 315 bits we care only about the higher end, not lower.
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// So like need to do high low mult with 2 U256's and then bitshift.
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// I bet this has a lot of room for multiplication optimization.
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const rhs_hi: u128 = 0x9392ee8e921d5d073aff322e62439fcf;
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const rhs_lo: u128 = 0x32d7f344649470f90cac0c573bf9e1b5;
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const ea = mul_u128(lhs_lo, rhs_lo);
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const gf = mul_u128(lhs_hi, rhs_lo);
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const jh = mul_u128(lhs_lo, rhs_hi);
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const lk = mul_u128(lhs_hi, rhs_hi);
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const e = ea.hi;
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const _a = ea.lo;
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const g = gf.hi;
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const f = gf.lo;
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const j = jh.hi;
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const h = jh.lo;
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const l = lk.hi;
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const k = lk.lo;
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// b = e + f + h
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var e_plus_f: u128 = undefined;
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overflowed = @addWithOverflow(u128, e, f, &e_plus_f);
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var b_carry1: u128 = undefined;
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if (overflowed) {
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b_carry1 = 1;
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} else {
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b_carry1 = 0;
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}
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var idk: u128 = undefined;
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overflowed = @addWithOverflow(u128, e_plus_f, h, &idk);
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var b_carry2: u128 = undefined;
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if (overflowed) {
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b_carry2 = 1;
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} else {
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b_carry2 = 0;
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}
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// c = carry + g + j + k // it doesn't say +k but I think it should be?
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var g_plus_j: u128 = undefined;
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overflowed = @addWithOverflow(u128, g, j, &g_plus_j);
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var c_carry1: u128 = undefined;
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if (overflowed) {
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c_carry1 = 1;
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} else {
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c_carry1 = 0;
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}
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var g_plus_j_plus_k: u128 = undefined;
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overflowed = @addWithOverflow(u128, g_plus_j, k, &g_plus_j_plus_k);
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var c_carry2: u128 = undefined;
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if (overflowed) {
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c_carry2 = 1;
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} else {
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c_carry2 = 0;
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}
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var c_without_bcarry2: u128 = undefined;
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overflowed = @addWithOverflow(u128, g_plus_j_plus_k, b_carry1, &c_without_bcarry2);
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var c_carry3: u128 = undefined;
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if (overflowed) {
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c_carry3 = 1;
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} else {
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c_carry3 = 0;
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}
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var c: u128 = undefined;
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overflowed = @addWithOverflow(u128, c_without_bcarry2, b_carry2, &c);
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var c_carry4: u128 = undefined;
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if (overflowed) {
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c_carry4 = 1;
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} else {
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c_carry4 = 0;
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}
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// d = carry + l
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var d: u128 = undefined;
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overflowed = @addWithOverflow(u128, l, c_carry1, &d);
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overflowed = overflowed or @addWithOverflow(u128, d, c_carry2, &d);
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overflowed = overflowed or @addWithOverflow(u128, d, c_carry3, &d);
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overflowed = overflowed or @addWithOverflow(u128, d, c_carry4, &d);
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if (overflowed) {
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std.debug.panic("TODO runtime exception for overflow!", .{});
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}
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// Final 512bit value is d, c, b, a
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// need to left shift 321 times
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// 315 - 256 is 59. So left shift d, c 59 times.
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return @intCast(i128, c >> 59 | (d << (128 - 59)));
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}
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fn mul_u128(a: u128, b: u128) U256 {
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var hi: u128 = undefined;
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var lo: u128 = undefined;
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const bits_in_dword_2: u32 = 64;
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const lower_mask: u128 = math.maxInt(u128) >> bits_in_dword_2;
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lo = (a & lower_mask) * (b & lower_mask);
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var t = lo >> bits_in_dword_2;
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lo &= lower_mask;
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t += (a >> bits_in_dword_2) * (b & lower_mask);
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lo += (t & lower_mask) << bits_in_dword_2;
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hi = t >> bits_in_dword_2;
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t = lo >> bits_in_dword_2;
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lo &= lower_mask;
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t += (b >> bits_in_dword_2) * (a & lower_mask);
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lo += (t & lower_mask) << bits_in_dword_2;
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hi += t >> bits_in_dword_2;
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hi += (a >> bits_in_dword_2) * (b >> bits_in_dword_2);
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return .{ .hi = hi, .lo = lo };
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}
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const one_e20: i256 = 100000000000000000000;
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const expectEqual = std.testing.expectEqual;
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test "add" {
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const dec: RocDec = .{ .num = 0 };
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expectEqual(RocDec{ .num = 0 }, dec.add(.{ .num = 0 }));
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}
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test "mul" {
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var dec1: RocDec = .{ .num = 0 };
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expectEqual(RocDec{ .num = 0 }, dec1.mul(.{ .num = 0 }));
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}
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