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Fix bigint multi-limb shift and masks

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This commit is contained in:
Marc Tiehuis 2018-05-05 22:40:29 +12:00
parent 87c0060e81
commit d7b029995c
2 changed files with 21 additions and 6 deletions
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10
src/bigint.cpp
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@ -1259,12 +1259,11 @@ void bigint_and(BigInt *dest, const BigInt *op1, const BigInt *op2) {
bigint_normalize(dest);
return;
}
// TODO this code path is untested
uint64_t first_digit = dest->data.digit;
dest->digit_count = max(op1->digit_count, op2->digit_count);
dest->data.digits = allocate_nonzero<uint64_t>(dest->digit_count);
dest->data.digits[0] = first_digit;
size_t i = 1;
size_t i = 0;
for (; i < op1->digit_count && i < op2->digit_count; i += 1) {
dest->data.digits[i] = op1_digits[i] & op2_digits[i];
}
@ -1412,7 +1411,6 @@ void bigint_shr(BigInt *dest, const BigInt *op1, const BigInt *op2) {
return;
}
// TODO this code path is untested
size_t digit_shift_count = shift_amt / 64;
size_t leftover_shift_count = shift_amt % 64;
@ -1427,7 +1425,7 @@ void bigint_shr(BigInt *dest, const BigInt *op1, const BigInt *op2) {
uint64_t digit = op1_digits[op_digit_index];
size_t dest_digit_index = op_digit_index - digit_shift_count;
dest->data.digits[dest_digit_index] = carry | (digit >> leftover_shift_count);
carry = (0xffffffffffffffffULL << leftover_shift_count) & digit;
carry = digit << leftover_shift_count;
if (dest_digit_index == 0) { break; }
op_digit_index -= 1;

17
test/cases/math.zig
View File

@ -349,6 +349,23 @@ test "big number shifting" {
}
}
test "big number multi-limb shift and mask" {
comptime {
var a = 0xefffffffa0000001eeeeeeefaaaaaaab;
assert(u32(a & 0xffffffff) == 0xaaaaaaab);
a >>= 32;
assert(u32(a & 0xffffffff) == 0xeeeeeeef);
a >>= 32;
assert(u32(a & 0xffffffff) == 0xa0000001);
a >>= 32;
assert(u32(a & 0xffffffff) == 0xefffffff);
a >>= 32;
assert(a == 0);
}
}
test "xor" {
test_xor();
comptime test_xor();