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// SPDX-License-Identifier: MPL-2.0
// (c) Hare authors <https://harelang.org>
// (c) 2010 The Go Authors. All rights reserved.
def maxshift: u8 = 60;
def decimal_point_range: u16 = 2047;
type decimal = struct {
// Numbers 0-9, not ascii, big endian. Length for small numbers is
// log10(mantissa * 5^-exp). Subnormal doubles have min exp -1074 and
// max mantissa 4e16, giving at most 767 digits.
digits: [800]u8,
// Number of valid digits. May be 0 if the number rounds to 0.
nd: size,
// Decimal point index, may be negative.
// -1 means 0.0ddd..., 0 means 0.ddd..., 1 means d.dd..., and so on.
dp: i32,
negative: bool,
// Were there nonzero digits beyond digits[0..nd]? This affects
// rounding.
truncated: bool,
};
// remove trailing zeroes
fn trim(d: *decimal) void = {
for (d.nd > 0 && d.digits[d.nd - 1] == 0) {
d.nd -= 1;
};
};
fn leftshift_newdigits(d: *decimal, shift: u32) u32 = {
shift &= 63;
let x_a = left_shift_table[shift]: u32;
let x_b = left_shift_table[shift + 1]: u32;
let nn = x_a >> 11;
let pow5_a = 0x7FF & x_a, pow5_b = 0x7FF & x_b;
const p5 = pow5_table[pow5_a..];
let i = 0u32, n = pow5_b - pow5_a;
for (i < n; i += 1) {
if (i >= d.nd) {
return nn - 1;
} else if (d.digits[i] == p5[i]) {
continue;
} else if (d.digits[i] < p5[i]) {
return nn - 1;
} else {
return nn;
};
};
return nn;
};
fn leftshift(d: *decimal, k: u32) void = {
assert(k <= maxshift);
if (d.nd == 0) return;
let nn = leftshift_newdigits(d, k);
let r = d.nd: int - 1, w = r: size + nn;
let n = 0u64;
for (r >= 0) {
n += d.digits[r]: u64 << k;
const quo = n / 10, rem = n - 10 * quo;
if (w < len(d.digits)) {
d.digits[w] = rem: u8;
} else if (rem != 0) {
d.truncated = true;
};
n = quo;
r -= 1;
w -= 1;
};
for (n > 0) {
const quo = n / 10, rem = n - 10 * quo;
if (w < len(d.digits)) {
d.digits[w] = rem: u8;
} else if (rem != 0) {
d.truncated = true;
};
n = quo;
w -= 1;
};
d.nd += nn;
if (d.nd > len(d.digits)) {
d.nd = len(d.digits);
};
d.dp += nn: i32;
trim(d);
};
fn rightshift(d: *decimal, k: u32) void = {
let r = 0z, w = 0z, n = 0u64;
for (n >> k == 0; r += 1) {
if (r >= d.nd) {
if (n == 0) {
d.nd = 0;
return;
};
for (n >> k == 0; r += 1) {
n *= 10;
};
break;
};
n = n * 10 + d.digits[r];
};
d.dp -= r: i32 - 1;
if (d.dp < -(decimal_point_range: i32)) {
*d = decimal { ... };
return;
};
const mask = (1u64 << k) - 1;
for (r < d.nd; r += 1) {
const dig = n >> k;
n &= mask;
d.digits[w] = dig: u8;
w += 1;
n = n * 10 + d.digits[r];
};
for (n > 0) {
const dig = n >> k;
n &= mask;
if (w < len(d.digits)) {
d.digits[w] = dig: u8;
w += 1;
} else if (dig > 0) {
d.truncated = true;
};
n *= 10;
};
d.nd = w;
trim(d);
};
// Shift right (k < 0) or left (k > 0). We can only shift up to 60 at a time
// without losing bits, so break up big shifts.
fn decimal_shift(d: *decimal, k: int) void = {
if (d.nd == 0) return;
if (k > 0) {
for (k > maxshift: int) {
leftshift(d, maxshift);
k -= maxshift: i32;
};
leftshift(d, k: u32);
} else if (k < 0) {
for (k < -(maxshift: int)) {
rightshift(d, maxshift);
k += maxshift: i32;
};
rightshift(d, (-k): u32);
};
};
fn should_round_up(d: *decimal, nd: uint) bool = if (nd < d.nd) {
if (d.digits[nd] == 5 && nd + 1 == d.nd) {
return d.truncated ||
(nd > 0 && d.digits[nd - 1] & 1 != 0);
} else return d.digits[nd] >= 5;
} else false;
fn round(d: *decimal, nd: uint) void = {
if (nd >= d.nd) return;
if (should_round_up(d, nd)) roundup(d, nd)
else rounddown(d, nd);
};
fn rounddown(d: *decimal, nd: uint) void = {
if (nd >= d.nd) return;
d.nd = nd;
trim(d);
};
fn roundup(d: *decimal, nd: uint) void = {
if (nd >= d.nd) return;
for (let i = nd: int - 1; i >= 0; i -= 1) {
if (d.digits[i] < 9) {
d.digits[i] += 1;
d.nd = i: size + 1;
return;
};
};
d.digits[0] = 1;
d.nd = 1;
d.dp += 1;
};
fn decimal_round(d: *decimal) u64 = {
if (d.nd == 0 || d.dp < 0) return 0;
if (d.dp > 18) return ~0u64;
let i = 0z, n: u64 = 0;
for (i < d.dp: uint && i < d.nd; i += 1) {
n = n * 10 + d.digits[i];
};
for (i < d.dp: uint; i += 1) {
n *= 10;
};
if (should_round_up(d, d.dp: uint)) {
n += 1;
};
return n;
};
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