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C: fixed-point analysis now tracks exponent of LSB rather than MSB
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This is in preparation for working with different word sizes in same
model. Would also allow the whole runtime to be compiled for a different
word size.
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@frothga
frothga committed May 13, 2024
1 parent 634f8dd commit 191f348
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Showing 63 changed files with 715 additions and 573 deletions.
92 changes: 49 additions & 43 deletions N2A/src/gov/sandia/n2a/backend/c/JobC.java
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7 changes: 3 additions & 4 deletions N2A/src/gov/sandia/n2a/backend/c/RendererC.java
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Original file line number Diff line number Diff line change
Expand Up @@ -164,8 +164,7 @@ public boolean render (Operator op)
}
else if (useExponent)
{
int shiftX = Operator.MSB - y.exponent;
int x = shiftX >= 0 ? 0x1 << shiftX : 0;
int x = y.exponent >= 0 ? 0x1 << y.exponent : 0;
result.append (", " + x);
}
}
Expand Down Expand Up @@ -249,14 +248,14 @@ else if (useExponent)
if (op instanceof Draw3D)
{
boolean needModel = ((Draw3D) d).needModelMatrix ();
int exponentP = Operator.MSB;
int exponentP = 0;
if (useExponent)
{
// position and model matrix share same exponent
Operator model = d.getKeyword ("model");
if (model != null) exponentP = model.exponentNext;
else if (d.operands.length > 1) exponentP = d.operands[1].exponentNext;
// else model has been initialized to identity, presumably integer 1. Operator.MSB set above is suitable default.
// else model has been initialized to identity, presumably integer 1. Zero set above is suitable default.
}

result.append (d.name + "->" + op + " (" + job.SIMULATOR + "currentEvent->t, material");
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38 changes: 17 additions & 21 deletions N2A/src/gov/sandia/n2a/backend/c/RendererCfp.java
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Original file line number Diff line number Diff line change
Expand Up @@ -192,9 +192,8 @@ public boolean render (Operator op)
OperatorBinary b = (OperatorBinary) op;

// Explanation of shift -- The exponent of the result will be the sum of the exponents
// of the two operands. That new exponent will be associated with bit position 2*MSB.
// We want the exponent at bit position MSB.
int exponentRaw = b.operand0.exponentNext + b.operand1.exponentNext - Operator.MSB; // Exponent at MSB position after a direct integer multiply.
// of the two operands.
int exponentRaw = b.operand0.exponentNext + b.operand1.exponentNext; // Exponent at LSB position after a direct integer multiply.
int shift = exponentRaw - b.exponentNext;

if (shift == 0)
Expand Down Expand Up @@ -266,8 +265,8 @@ public boolean render (Operator op)
// Explanation of shift -- In a division, the quotient is effectively down-shifted by
// the number of bits in the denominator, and its exponent is the difference between
// the exponents of the numerator and denominator. In A/B, exponentA-exponentB will
// be the exponent at bit position 0. We want the exponent at bit position MSB.
int exponentRaw = d.operand0.exponentNext - d.operand1.exponentNext + Operator.MSB; // Exponent in MSB from a direct integer division.
// be the exponent at bit position 0.
int exponentRaw = d.operand0.exponentNext - d.operand1.exponentNext; // Exponent in LSB from a direct integer division.
int shift = exponentRaw - d.exponentNext;

if (shift == 0)
Expand Down Expand Up @@ -395,22 +394,21 @@ public boolean render (Operator op)
{
Ceil c = (Ceil) op;
Operator a = c.operands[0];
if (a.exponent >= Operator.MSB) // LSB is above decimal, so ceil() operation is impossible. This test must be on a.exponent rather than a.exponentNext because ...
if (a.exponent >= 0) // LSB is above decimal, so ceil() operation is impossible. This test must be on a.exponent rather than a.exponentNext because ...
{
// a.exponentNext has been set to f.exponentNext by Round.determineExponentNextStatic(),
// so no shift is necessary.
a.render (this);
}
else // a.exponentNext is in [0, MSB), as enforced by Round.determineExponentNextStatic()
else // a.exponentNext is in [-MSB, -1], as enforced by Round.determineExponentNextStatic()
{
// Create a mask for bits below the decimal point.
// When this mask is added to the number, it will add 1 to the first bit position
// above the decimal if any bit is set under the mask. Afterward, used AND to remove
// any residual bits below the decimal.
// This works for both positive and negative numbers.
int shift = a.exponentNext - c.exponentNext;
int decimalPlaces = Operator.MSB - a.exponentNext;
int wholeMask = 0xFFFFFFFF << decimalPlaces;
int wholeMask = 0xFFFFFFFF << -a.exponentNext;
int decimalMask = ~wholeMask;

if (shift != 0) result.append ("(");
Expand Down Expand Up @@ -456,8 +454,7 @@ public boolean render (Operator op)
if (op.parent == null || op.parent instanceof OperatorLogicalInput) return super.render (op);

Event e = (Event) op;
int exponentRaw = Operator.MSB - e.eventType.valueIndex;
int shift = exponentRaw - e.exponentNext;
int shift = -e.eventType.valueIndex - e.exponentNext;

if (shift != 0) result.append ("(");
result.append ("(flags & (" + bed.localFlagType + ") 0x1 << " + e.eventType.valueIndex + ")");
Expand All @@ -473,16 +470,15 @@ public boolean render (Operator op)
// See Ceil above for similar code.
Floor f = (Floor) op;
Operator a = f.operands[0];
if (a.exponent >= Operator.MSB)
if (a.exponent >= 0)
{
a.render (this);
}
else
{
// Mask off bits below the decimal point. This works for both positive and negative numbers.
int shift = a.exponentNext - f.exponentNext;
int decimalPlaces = Operator.MSB - a.exponentNext;
int wholeMask = 0xFFFFFFFF << decimalPlaces;
int wholeMask = 0xFFFFFFFF << -a.exponentNext;

if (shift != 0) result.append ("(");
result.append ("(");
Expand Down Expand Up @@ -528,14 +524,14 @@ public boolean render (Operator op)
// See Ceil above for similar code.
Round r = (Round) op;
Operator a = r.operands[0];
if (a.exponent >= Operator.MSB)
if (a.exponent >= 0)
{
a.render (this);
}
else // a.exponentNext in [0, MSB)
else // a.exponentNext in [-MSB, -1]
{
int shift = a.exponentNext - r.exponentNext;
int decimalPlaces = Operator.MSB - a.exponentNext;
int decimalPlaces = -a.exponentNext;
int mask = 0xFFFFFFFF << decimalPlaces;
int half = 0x1 << decimalPlaces - 1;

Expand All @@ -555,7 +551,7 @@ public boolean render (Operator op)
{
Signum s = (Signum) op;
Operator a = s.operands[0];
int one = 0x1 << Operator.MSB - s.exponentNext;
int one = 0x1 << -s.exponentNext;
boolean needParens = a.precedence () >= new LT ().precedence ();
if (needParens) result.append ("(");
a.render (this);
Expand Down Expand Up @@ -609,14 +605,14 @@ public boolean provides64bit (Operator op)
if (op instanceof Multiply)
{
OperatorBinary b = (OperatorBinary) op;
int exponentRaw = b.operand0.exponentNext + b.operand1.exponentNext - Operator.MSB;
int exponentRaw = b.operand0.exponentNext + b.operand1.exponentNext;
int shift = exponentRaw - b.exponentNext;
return shift < 0; // only use 64-bit when we downshift the raw result
}
if (op instanceof Divide)
{
OperatorBinary b = (OperatorBinary) op;
int exponentRaw = b.operand0.exponentNext - b.operand1.exponentNext + Operator.MSB;
int exponentRaw = b.operand0.exponentNext - b.operand1.exponentNext;
int shift = exponentRaw - b.exponentNext;
return shift > 0; // only use 64-bit when we upshift the raw result
}
Expand Down Expand Up @@ -665,7 +661,7 @@ public String print (double d, int exponent)
bits |= 0x10000000000000l; // set implied msb of mantissa (bit 52) to 1
bits &= 0x1FFFFFFFFFFFFFl; // clear sign and exponent bits
if (negate) bits = -bits;
bits >>= 52 - Operator.MSB + exponent - e;
bits >>= 52 + exponent - e;
return Integer.toString ((int) bits);
}
}
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