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Fix dec division problem

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Fixed dec division that envolves a number that has a hi word greater than
0 when converted into `U256` like `341dec / 341`.

This commit resolves #5259
This commit is contained in:
Yuki Omoto 2023-04-08 23:51:11 +09:00
parent e5d13bfc22
commit 219e72ff20
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GPG key ID: 9A7D6C91D5219717
1 changed files with 54 additions and 7 deletions
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61
crates/compiler/builtins/bitcode/src/dec.zig
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@ -553,7 +553,7 @@ fn mul_and_decimalize(a: u128, b: u128) i128 {
// Multiply two 128-bit ints and divide the result by 10^DECIMAL_PLACES
//
// Adapted from https://github.com/nlordell/ethnum-rs
// Adapted from https://github.com/nlordell/ethnum-rs/blob/c9ed57e131bffde7bcc8274f376e5becf62ef9ac/src/intrinsics/native/divmod.rs
// Copyright (c) 2020 Nicholas Rodrigues Lordello
// Licensed under the Apache License version 2.0
//
@ -656,6 +656,9 @@ fn div_u256_by_u128(numer: U256, denom: u128) U256 {
// 1 <= sr <= N_UTWORD_BITS - 1
var carry: u128 = 0;
const i128_max: i128 = 170141183460469231731687303715884105727;
const i128_min: i128 = -170141183460469231731687303715884105728;
const u128_max: u128 = 340282366920938463463374607431768211455;
while (sr > 0) {
// r:q = ((r:q) << 1) | carry
r.hi = (r.hi << 1) | (r.lo >> (N_UDWORD_BITS - 1));
@ -682,16 +685,34 @@ fn div_u256_by_u128(numer: U256, denom: u128) U256 {
lo_overflowed = @subWithOverflow(u128, lo, 1, &lo);
hi = hi -% @intCast(u128, @bitCast(u1, lo_overflowed));
// TODO this U256 was originally created by:
// NOTE: this U256 was originally created by:
//
// ((hi as i128) >> 127).as_u256()
//
// ...however, I can't figure out where that function is defined.
// Maybe it's defined using a macro or something. Anyway, hopefully
// this is what it would do in this scenario.
// As an implementation of `as_u256`, we wrap a negative value around to the maximum value of U256.
var hi_i128: i128 = undefined;
if (hi > i128_max) {
var overflowed_amount: u128 = hi - @intCast(u128, i128_max) - 1;
var overflowed_amount_i128 = @intCast(i128, overflowed_amount);
hi_i128 = i128_min + overflowed_amount_i128;
} else {
hi_i128 = @intCast(i128, hi);
}
var s_i128: i128 = math.shr(i128, hi_i128, 127);
var s_i128_abs = math.absInt(s_i128) catch unreachable;
var s_hi: u128 = undefined;
var s_lo: u128 = undefined;
if (s_i128 < 0) {
s_hi = u128_max;
s_lo = u128_max - @intCast(u128, (s_i128_abs - 1));
} else {
s_hi = 0;
s_lo = @intCast(u128, s_i128_abs);
}
var s = .{
.hi = 0,
.lo = math.shr(u128, hi, 127),
.hi = s_hi,
.lo = s_lo,
};
carry = s.lo & 1;
@ -1055,6 +1076,32 @@ test "div: 10 / 3" {
try expectEqual(res, numer.div(denom));
}
test "div: 341 / 341" {
var number1: RocDec = RocDec.fromU64(341);
var number2: RocDec = RocDec.fromU64(341);
try expectEqual(RocDec.fromU64(1), number1.div(number2));
}
test "div: 342 / 343" {
var number1: RocDec = RocDec.fromU64(342);
var number2: RocDec = RocDec.fromU64(343);
var roc_str = RocStr.init("0.997084548104956268", 20);
try expectEqual(RocDec.fromStr(roc_str), number1.div(number2));
}
test "div: 680 / 340" {
var number1: RocDec = RocDec.fromU64(680);
var number2: RocDec = RocDec.fromU64(340);
try expectEqual(RocDec.fromU64(2), number1.div(number2));
}
test "div: 500 / 1000" {
var number1: RocDec = RocDec.fromU64(500);
var number2: RocDec = RocDec.fromU64(1000);
var roc_str = RocStr.init("0.5", 3);
try expectEqual(RocDec.fromStr(roc_str), number1.div(number2));
}
// exports
pub fn fromStr(arg: RocStr) callconv(.C) num_.NumParseResult(i128) {