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Add functions for 32-bit floating point addition
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Also adds operation for 32-bit floating point addition instruction.
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@ShashankVM
ShashankVM committed Dec 1, 2024
1 parent 1d7d655 commit 8ab0ce0
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Showing 2 changed files with 93 additions and 23 deletions.
5 changes: 2 additions & 3 deletions arch/inst/F/fadd.s.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -26,9 +26,8 @@ access:
vu: always
data_independent_timing: true
operation(): |
RoundingMode mode = rm_to_mode(X[rm], $encoding);
X[fd] = f32_add(X[fs1], X[fs2], mode);
sail(): |
{
Expand Down
111 changes: 91 additions & 20 deletions arch/isa/fp.idl
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Original file line number Diff line number Diff line change
Expand Up @@ -489,7 +489,7 @@ function softfloat_normRoundPackToF32 {
function signF32UI {
returns Bits<1>
arguments
Bits<32> a,
Bits<32> a
description {
Extract sign-bit of a 32-bit floating point number
}
Expand All @@ -501,7 +501,7 @@ function signF32UI {
function expF32UI {
returns Bits<8>
arguments
Bits<32> a,
Bits<32> a
description {
Extract exponent of a 32-bit floating point number
}
Expand All @@ -513,7 +513,7 @@ function expF32UI {
function fracF32UI {
returns Bits<23>
arguments
Bits<32> a,
Bits<32> a
description {
Extract significand of a 32-bit floating point number
}
Expand Down Expand Up @@ -590,14 +590,14 @@ function softfloat_propagateNaNF32UI {
}
body {
# check if a and b are signalling
Boolean isSigNaN_a = is_sp_signaling_nan(a);
Boolean isSigNaN_b = is_sp_signaling_nan(b);
Boolean isSigNaN_a = is_sp_signaling_nan?(a);
Boolean isSigNaN_b = is_sp_signaling_nan?(b);

# get non Signalling versions of a and b
U32 nonsig_a = returnNonSignalingNaN(a);
U32 nonsig_b = returnNonSignalingNaN(b);

if (isSigNaN_a | isSigNaN_b) {
if (isSigNaN_a || isSigNaN_b) {
# raise invalid flag if either number is NaN
set_fp_flag(FpFlag::NV);
if ( isSigNaN_a ) {
Expand All @@ -606,9 +606,9 @@ function softfloat_propagateNaNF32UI {
return returnLargerMag(a, b);
}
# if b is NaN return non signaling value of b
return is_sp_nan(b) ? nonsig_b : nonsig_a;
return is_sp_nan?(b) ? nonsig_b : nonsig_a;
} else {
return is_sp_nan(a) ? nonsig_a : nonsig_b;
return is_sp_nan?(a) ? nonsig_a : nonsig_b;
}
}

Expand Down Expand Up @@ -643,7 +643,7 @@ function softfloat_addMagsF32 {
Bits<8> expZ;

# calculate difference of exponents
Bits<8> expDiff = expA - expB
Bits<8> expDiff = expA - expB;

if (expDiff == 8'd0) {
if (expA == 8'd0) {
Expand All @@ -654,8 +654,8 @@ function softfloat_addMagsF32 {
# check if A is infinity or NaN
if (expA == 8'hFF) {
# A is NaN if significand is non-zero and exponent is 8'hFF
if ((sigA != 8'd0) | (sigB != 8'd0)) {
softfloat_propagateNaNF32UI(a, b);
if ((sigA != 8'd0) || (sigB != 8'd0)) {
return softfloat_propagateNaNF32UI(a, b);
}
# return infinity if A is infinity
return a;
Expand Down Expand Up @@ -687,7 +687,7 @@ function softfloat_addMagsF32 {
if (expB == 8'hFF) {
# B is NaN if exponent is 8'hFF and significand is non-zero
if (sigB != 0) {
softfloat_propagateNaNF32UI(a, b);
return softfloat_propagateNaNF32UI(a, b);
}
# return infinity with same sign as A
return packToF32UI(signZ, 8'hFF, 23'h0);
Expand All @@ -701,7 +701,7 @@ function softfloat_addMagsF32 {
if (expA == 8'hFF) {
# A is NaN if exponent is 8'hFF and significand is non-zero
if (sigA != 0) {
softfloat_propagateNaNF32UI(a, b);
return softfloat_propagateNaNF32UI(a, b);
}
# return infinity with same sign as A
return a;
Expand Down Expand Up @@ -752,19 +752,27 @@ function softfloat_subMagsF32 {
# declare a variable to store the difference in significand
U32 sigDiff;

# declare a sigX and sigY
U32 sigX;
U32 sigY;

# declare a U32 sigA and sigB
U32 sigA_32;
U32 sigB_32;

# declare a variable to store shift distance
Bits<8> shiftDist;

# calculate difference of exponents
Bits<8> expDiff = expA - expB
Bits<8> expDiff = expA - expB;

if (expDiff == 8'd0) {

# check if A is infinity or NaN
if (expA == 8'hFF) {
# A is NaN if significand is non-zero and exponent is 8'hFF
if ((sigA != 8'd0) | (sigB != 8'd0)) {
softfloat_propagateNaNF32UI(a, b);
if ((sigA != 8'd0) || (sigB != 8'd0)) {
return softfloat_propagateNaNF32UI(a, b);
}
# return infinity if A is infinity
return a;
Expand All @@ -775,18 +783,81 @@ function softfloat_subMagsF32 {
# check if no difference in significand
if (sigDiff == 0) {
# return -0 if rounding mode is round down, else return +0
return packToF32UI((mode == RoundingMode::RDN),0,0);
return packToF32UI(((mode == RoundingMode::RDN) ? 1 : 0),0,0);
}

if (expA != 0) {
expA = expA - 1;
}

signZ = signF32UI(a);

# if difference is negative, change the sign of the result
if (sigDiff < 0) {
signZ != signZ;
sigDiff = -32'hs1 * sigDiff;
signZ = ~signZ;
sigDiff = -32'sh1 * sigDiff;
}


shiftDist = count_leading_zeros<32>(sigDiff) - 8;
expZ = expA - shiftDist;

if (expZ < 0) {
shiftDist = expA;
expZ = 0;
}

return packToF32UI(signZ, expZ, sigDiff << shiftDist);

} else {
# when difference in exponents are not zero
signZ = signF32UI(a);
sigA_32 = 32'h0 + (sigA << 7);
sigB_32 = 32'h0 + (sigB << 7);
if (expDiff < 0) {
signZ = ~signZ;
if (expB == 0xFF) {
if (sigB_32 != 0) {
return softfloat_propagateNaNF32UI(a, b);
}
return packToF32UI(signZ, expB, 0);
}
expZ = expB - 1;
sigX = sigB_32 | 0x40000000;
sigY = sigA_32 + ((expA != 0) ? 0x40000000 : sigA_32);
expDiff = - expDiff;
} else {
if (expA == 0xFF) {
if (sigA_32 != 0) {
return softfloat_propagateNaNF32UI(a, b);
}
return a;
}
expZ = expA - 1;
sigX = sigA_32 | 0x40000000;
sigY = sigB_32 + ((expB != 0) ? 0x40000000 : sigB_32);
}
return softfloat_normRoundPackToF32(signZ, expZ, sigX - softfloat_shiftRightJam32(sigY, expDiff), mode);
}
}
}

function f32_add {
returns U32
arguments
U32 a,
U32 b,
RoundingMode mode
description {
Returns sum of 2 floating point numbers
}
body {
U32 a_xor_b = a ^ b;
if (signF32UI(a_xor_b) == 1) {
# subtract if signs are different
return softfloat_subMagsF32(a,b,mode);
} else {
# add if signs are the same
return softfloat_addMagsF32(a,b,mode);
}
}
}

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