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An apparently faster iteration of CSetBounds.

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This commit is contained in:
Jonathan Woodruff
2020-03-02 16:10:33 +00:00
parent 42cdd2e3da
commit ebac2cdf6d
1 changed files with 5 additions and 4 deletions
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9
CHERICC_Fat.bsv
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@@ -478,8 +478,10 @@ function SetBoundsReturn setBoundsFat(CapFat cap, Address lengthFull);
// Finally check how close the requested length is to overflow, and test in relation to how much the
// length will increase.
LCapAddress topLo = (lmaskLor & len) + (lmaskLor & base);
Bool lengthCarryIn = (~lmaskLor & topLo) != 0;
Bool lengthRoundUp = (lmaskLor & topLo) != 0;
LCapAddress mwLsbMask = lmaskLor ^ lmaskLo;
// If the first bit of the mantissa of the top is not the sum of the corrosponding bits of base and length, there was a carry in.
Bool lengthCarryIn = (mwLsbMask & top) != ((mwLsbMask & base)^(mwLsbMask & len));
Bool lengthRoundUp = lostSignificantTop;
Bool lengthIsMax = (len & (~lmaskLor)) == (lmask ^ lmaskLor);
Bool lengthIsMaxLessOne = (len & (~lmaskLor)) == (lmask ^ lmaskLo);
@@ -488,13 +490,11 @@ function SetBoundsReturn setBoundsFat(CapFat cap, Address lengthFull);
if (lengthIsMaxLessOne && lengthCarryIn && lengthRoundUp) lengthOverflow = True;
Bool exact = True;
LCapAddress baseMask = ~lmaskLor;
if(lengthOverflow && intExp) begin
e = e+1;
ret.bounds.topBits = (lostSignificantTopHigher) ? (newTopBitsHigher+'b1000):newTopBitsHigher;
ret.bounds.baseBits = truncateLSB(newBaseBits);
exact = !(lostSignificantBaseHigher || lostSignificantTopHigher);
baseMask = ~lmaskLo;
end else begin
ret.bounds.topBits = (lostSignificantTop) ? truncate(newTopBits+'b1000):truncate(newTopBits);
ret.bounds.baseBits = truncate(newBaseBits);
@@ -524,6 +524,7 @@ function SetBoundsReturn setBoundsFat(CapFat cap, Address lengthFull);
newLengthRounded = (newLengthRounded & (~lmaskLor));
if (lostSignificantLen) newLength = newLengthRounded;
end
LCapAddress baseMask = ~lmaskLor;
// Return derived capability
return SetBoundsReturn{cap: ret, exact: exact, length: truncate(newLength), mask: truncate(baseMask)};