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Values for IEEE 754 vs. RISC-V Table 11.4 in the RISC-V Unprivileged ISA

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James E. Stine 2024-01-14 22:08:42 -06:00
parent f267c20601
commit b14cd67bef
1 changed files with 52 additions and 11 deletions
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63
src/fpu/postproc/specialcase.sv
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@ -266,6 +266,30 @@ module specialcase import cvw::*; #(parameter cvw_t P) (
// integer result selection
///////////////////////////////////////////////////////////////////////////////////////
// Causes undefined behavior for invalid:
// Invalid cases are different for IEEE 754 vs. RISC-V. For RISC-V, typical results are used
// unsigned: if invalid (e.g., negative fp to unsigned int, result should overflow and
// overflows to the maximum value
// signed: if invalid, result should overflow to maximum negative value
// but is undefined and used for information only
// Note: The IEEE 754 result comes from values in TestFloat for x86_64
// IEEE 754
// select the overflow integer res
// - negitive infinity and out of range negitive input
// | int | long |
// signed | -2^31 | -2^63 |
// unsigned | 2^32-1 | 2^64-1 |
//
// - positive infinity and out of range positive input and NaNs
// | int | long |
// signed | -2^31 |-2^63 |
// unsigned | 2^32-1 | 2^64-1 |
//
// other: 32 bit unsigned res should be sign extended as if it were a signed number
// RISC-V
// select the overflow integer res
// - negitive infinity and out of range negitive input
// | int | long |
@ -278,17 +302,34 @@ module specialcase import cvw::*; #(parameter cvw_t P) (
// unsigned | 2^32-1 | 2^64-1 |
//
// other: 32 bit unsinged res should be sign extended as if it were a signed number
always_comb
if(Signed)
if(Xs&~NaNIn) // signed negitive
if(Int64) OfIntRes = {1'b1, {P.XLEN-1{1'b0}}};
else OfIntRes = {{P.XLEN-32{1'b1}}, 1'b1, {31{1'b0}}};
else // signed positive
if(Int64) OfIntRes = {1'b0, {P.XLEN-1{1'b1}}};
else OfIntRes = {{P.XLEN-32{1'b0}}, 1'b0, {31{1'b1}}};
else
if(Xs&~NaNIn) OfIntRes = {P.XLEN{1'b0}}; // unsigned negitive
else OfIntRes = {P.XLEN{1'b1}}; // unsigned positive
if(P.IEEE754) begin
always_comb
if(Signed)
if(Xs&~NaNIn) // signed negitive
if(Int64) OfIntRes = {1'b1, {P.XLEN-1{1'b0}}};
else OfIntRes = {{P.XLEN-32{1'b1}}, 1'b1, {31{1'b0}}};
else // signed positive
if(Int64) OfIntRes = {1'b1, {P.XLEN-1{1'b0}}};
else OfIntRes = {{P.XLEN-32{1'b1}}, 1'b1, {31{1'b0}}};
else
if(Xs&~NaNIn) OfIntRes = {P.XLEN{1'b1}}; // unsigned negitive
else OfIntRes = {P.XLEN{1'b1}}; // unsigned positive
end // if (P.IEEE754)
else begin
always_comb
if(Signed)
if(Xs&~NaNIn) // signed negitive
if(Int64) OfIntRes = {1'b1, {P.XLEN-1{1'b0}}};
else OfIntRes = {{P.XLEN-32{1'b1}}, 1'b1, {31{1'b0}}};
else // signed positive
if(Int64) OfIntRes = {1'b0, {P.XLEN-1{1'b1}}};
else OfIntRes = {{P.XLEN-32{1'b0}}, 1'b0, {31{1'b1}}};
else
if(Xs&~NaNIn) OfIntRes = {P.XLEN{1'b0}}; // unsigned negitive
else OfIntRes = {P.XLEN{1'b1}}; // unsigned positive
end // else: !if(P.IEEE754)
// select the integer output
// - if the input is invalid (out of bounds NaN or Inf) then output overflow res