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Make the verinum pow operator work correctly. 

The functionality of the integer power operator is specified in
1364-2005 on page 45-46 and specifically Table 5-6. This patch
fixes the verinum pow operator to work as specified in this
table. It also fixes an error in the == operator when both
operators are signed and only the left argument is negative.
This commit is contained in:
Cary R 2009-12-05 21:49:32 -08:00 committed by Stephen Williams
parent 59ebd47ba6
commit eea816e423
1 changed files with 40 additions and 4 deletions
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44
verinum.cc
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@ -1,5 +1,5 @@
/* /*
* Copyright (c) 1998-2008 Stephen Williams (steve@icarus.com) * Copyright (c) 1998-2009 Stephen Williams (steve@icarus.com)
* *
* This source code is free software; you can redistribute it * This source code is free software; you can redistribute it
* and/or modify it in source code form under the terms of the GNU * and/or modify it in source code form under the terms of the GNU
@ -746,7 +746,7 @@ verinum::V operator == (const verinum&left, const verinum&right)
right_pad = right.get(right.len()-1); right_pad = right.get(right.len()-1);
if (left_pad == verinum::V1 && right_pad == verinum::V0) if (left_pad == verinum::V1 && right_pad == verinum::V0)
return verinum::V1; return verinum::V0;
if (left_pad == verinum::V0 && right_pad == verinum::V1) if (left_pad == verinum::V0 && right_pad == verinum::V1)
return verinum::V0; return verinum::V0;
} }
@ -1051,9 +1051,45 @@ verinum operator * (const verinum&left, const verinum&right)
verinum pow(const verinum&left, const verinum&right) verinum pow(const verinum&left, const verinum&right)
{ {
verinum result = left; verinum result = left;
unsigned pow_count = right.as_ulong(); long pow_count = right.as_long();
for (unsigned idx = 1 ; idx < pow_count ; idx += 1) // We need positive and negative one in a few places.
verinum one (verinum::V0, left.len(), left.has_len());
one.has_sign(left.has_sign());
one.set(0, verinum::V1);
verinum m_one (verinum::V1, left.len(), left.has_len());
m_one.has_sign(true);
// If either the right or left values are undefined we return 'bx.
if (!right.is_defined() || !left.is_defined()) {
result = verinum(verinum::Vx, left.len(), left.has_len());
result.has_sign(left.has_sign());
// If the right value is zero we need to set the result to 1.
} else if (pow_count == 0) {
result = one;
} else if (pow_count < 0) {
// 0 ** <negative> is 'bx.
if (left.is_zero()) {
result = verinum(verinum::Vx, left.len(), left.has_len());
result.has_sign(left.has_sign());
// 1 ** <negative> is 1.
} else if (left == one) {
result = one;
// -1 ** <negative> is 1 or -1.
} else if (left.has_sign() && left == m_one) {
if (pow_count%2 == 0) {
result = one;
} else {
result = m_one;
}
// Everything else is 0.
} else {
result = verinum(verinum::V0, left.len(), left.has_len());
result.has_sign(left.has_sign());
}
}
for (long idx = 1 ; idx < pow_count ; idx += 1)
result = result * left; result = result * left;
return result; return result;