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FPU: Decide on A input selection a cycle earlier

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This moves opsel_a into the reg_type record, meaning that the A
multiplexer input now needs to be decided a cycle earlier.  This helps
timing by eliminating the combinatorial path from r.state and other
things to opsel_a and thence to in_a and result.

This means that some things now take an extra cycle, in particular
some of the exception cases such as when one or both operands are
NaNs.  The NaN handling has been moved out to its own state, which
simplifies the logic for exception cases in other places.  Additions
or subtractions where FRB's exponent is smaller than FRA's will
also take an extra cycle.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/245/head
Paul Mackerras 4 years ago
parent b0b3c0dc70
commit fb5115c944
1 changed files with 177 additions and 153 deletions
Show Stats Download Patch File Download Diff File

320
fpu.vhdl
Unescape Escape View File

@ -44,7 +44,7 @@ architecture behaviour of fpu is
DO_FRE, DO_FRSQRTE,
DO_FSEL,
FRI_1,
ADD_SHIFT, ADD_2, ADD_3,
ADD_1, ADD_SHIFT, ADD_2, ADD_3,
CMP_1, CMP_2,
MULT_1,
FMADD_1, FMADD_2, FMADD_3,
@ -65,7 +65,8 @@ architecture behaviour of fpu is
DENORM,
RENORM_A, RENORM_A2,
RENORM_B, RENORM_B2,
RENORM_C, RENORM_C2);
RENORM_C, RENORM_C2,
NAN_RESULT, EXC_RESULT);

type reg_type is record
state : state_t;
@ -111,6 +112,12 @@ architecture behaviour of fpu is
first : std_ulogic;
count : unsigned(1 downto 0);
doing_ftdiv : std_ulogic_vector(1 downto 0);
opsel_a : std_ulogic_vector(1 downto 0);
use_a : std_ulogic;
use_b : std_ulogic;
use_c : std_ulogic;
invalid : std_ulogic;
negate : std_ulogic;
end record;

type lookup_table is array(0 to 1023) of std_ulogic_vector(17 downto 0);
@ -118,7 +125,6 @@ architecture behaviour of fpu is
signal r, rin : reg_type;

signal fp_result : std_ulogic_vector(63 downto 0);
signal opsel_a : std_ulogic_vector(1 downto 0);
signal opsel_b : std_ulogic_vector(1 downto 0);
signal opsel_r : std_ulogic_vector(1 downto 0);
signal opsel_s : std_ulogic_vector(1 downto 0);
@ -724,7 +730,7 @@ begin
v.update_fprf := '0';
v.shift := to_signed(0, EXP_BITS);
v.first := '0';
opsel_a <= AIN_R;
v.opsel_a := AIN_R;
opsel_ainv <= '0';
opsel_amask <= '0';
opsel_b <= BIN_ZERO;
@ -758,6 +764,11 @@ begin
shiftin := '0';
case r.state is
when IDLE =>
v.use_a := '0';
v.use_b := '0';
v.use_c := '0';
v.invalid := '0';
v.negate := '0';
if e_in.valid = '1' then
case e_in.insn(5 downto 1) is
when "00000" =>
@ -770,6 +781,7 @@ begin
elsif e_in.insn(7) = '1' then
v.state := DO_MCRFS;
else
v.opsel_a := AIN_B;
v.state := DO_FCMP;
end if;
when "00110" =>
@ -789,14 +801,17 @@ begin
v.state := DO_MTFSF;
end if;
when "01000" =>
v.opsel_a := AIN_B;
if e_in.insn(9 downto 8) /= "11" then
v.state := DO_FMR;
else
v.state := DO_FRI;
end if;
when "01100" =>
v.opsel_a := AIN_B;
v.state := DO_FRSP;
when "01110" =>
v.opsel_a := AIN_B;
if int_input = '1' then
-- fcfid[u][s]
v.state := DO_FCFID;
@ -805,25 +820,45 @@ begin
end if;
when "01111" =>
v.round_mode := "001";
v.opsel_a := AIN_B;
v.state := DO_FCTI;
when "10010" =>
v.opsel_a := AIN_A;
if v.b.mantissa(54) = '0' and v.a.mantissa(54) = '1' then
v.opsel_a := AIN_B;
end if;
v.state := DO_FDIV;
when "10100" | "10101" =>
v.opsel_a := AIN_A;
v.state := DO_FADD;
when "10110" =>
v.is_sqrt := '1';
v.opsel_a := AIN_B;
v.state := DO_FSQRT;
when "10111" =>
v.state := DO_FSEL;
when "11000" =>
v.opsel_a := AIN_B;
v.state := DO_FRE;
when "11001" =>
v.is_multiply := '1';
v.opsel_a := AIN_A;
if v.c.mantissa(54) = '0' and v.a.mantissa(54) = '1' then
v.opsel_a := AIN_C;
end if;
v.state := DO_FMUL;
when "11010" =>
v.is_sqrt := '1';
v.opsel_a := AIN_B;
v.state := DO_FRSQRTE;
when "11100" | "11101" | "11110" | "11111" =>
if v.a.mantissa(54) = '0' then
v.opsel_a := AIN_A;
elsif v.c.mantissa(54) = '0' then
v.opsel_a := AIN_C;
else
v.opsel_a := AIN_B;
end if;
v.state := DO_FMADD;
when others =>
illegal := '1';
@ -880,11 +915,10 @@ begin

when DO_FCMP =>
-- fcmp[uo]
-- r.opsel_a = AIN_B
v.instr_done := '1';
v.state := IDLE;
update_fx := '1';
opsel_a <= AIN_B;
opsel_r <= RES_SUM;
v.result_exp := r.b.exponent;
if (r.a.class = NAN and r.a.mantissa(53) = '0') or
(r.b.class = NAN and r.b.mantissa(53) = '0') then
@ -930,6 +964,7 @@ begin
-- Prepare to subtract mantissas, put B in R
v.cr_result := "0000";
v.instr_done := '0';
v.opsel_a := AIN_A;
v.state := CMP_1;
end if;
v.fpscr(FPSCR_FL downto FPSCR_FU) := v.cr_result;
@ -1017,7 +1052,7 @@ begin
v.state := IDLE;

when DO_FMR =>
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B
v.result_class := r.b.class;
v.result_exp := r.b.exponent;
v.quieten_nan := '0';
@ -1037,7 +1072,7 @@ begin
v.state := IDLE;

when DO_FRI => -- fri[nzpm]
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B
v.result_class := r.b.class;
v.result_sign := r.b.negative;
v.result_exp := r.b.exponent;
@ -1062,7 +1097,7 @@ begin
end if;

when DO_FRSP =>
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B, r.shift = 0
v.result_class := r.b.class;
v.result_sign := r.b.negative;
v.result_exp := r.b.exponent;
@ -1092,7 +1127,7 @@ begin
-- instr bit 9: 1=dword 0=word
-- instr bit 8: 1=unsigned 0=signed
-- instr bit 1: 1=round to zero 0=use fpscr[RN]
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B
v.result_class := r.b.class;
v.result_sign := r.b.negative;
v.result_exp := r.b.exponent;
@ -1130,8 +1165,8 @@ begin
end case;

when DO_FCFID =>
-- r.opsel_a = AIN_B
v.result_sign := '0';
opsel_a <= AIN_B;
if r.insn(8) = '0' and r.b.negative = '1' then
-- fcfid[s] with negative operand, set R = -B
opsel_ainv <= '1';
@ -1150,16 +1185,19 @@ begin

when DO_FADD =>
-- fadd[s] and fsub[s]
opsel_a <= AIN_A;
-- r.opsel_a = AIN_A
v.result_sign := r.a.negative;
v.result_class := r.a.class;
v.result_exp := r.a.exponent;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
v.use_a := '1';
v.use_b := '1';
is_add := r.a.negative xor r.b.negative xor r.insn(1);
if r.a.class = FINITE and r.b.class = FINITE then
v.is_subtract := not is_add;
v.add_bsmall := r.exp_cmp;
v.opsel_a := AIN_B;
if r.exp_cmp = '0' then
v.shift := r.a.exponent - r.b.exponent;
v.result_sign := r.b.negative xnor r.insn(1);
@ -1169,77 +1207,55 @@ begin
v.state := ADD_SHIFT;
end if;
else
opsel_a <= AIN_B;
v.shift := r.b.exponent - r.a.exponent;
v.result_exp := r.b.exponent;
v.state := ADD_SHIFT;
v.state := ADD_1;
end if;
else
if (r.a.class = NAN and r.a.mantissa(53) = '0') or
(r.b.class = NAN and r.b.mantissa(53) = '0') then
-- Signalling NAN
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
if r.a.class = NAN then
-- nothing to do, result is A
elsif r.b.class = NAN then
v.result_class := NAN;
v.result_sign := r.b.negative;
opsel_a <= AIN_B;
if r.a.class = NAN or r.b.class = NAN then
v.state := NAN_RESULT;
elsif r.a.class = INFINITY and r.b.class = INFINITY and is_add = '0' then
-- invalid operation, construct QNaN
v.fpscr(FPSCR_VXISI) := '1';
qnan_result := '1';
arith_done := '1';
elsif r.a.class = ZERO and r.b.class = ZERO and is_add = '0' then
-- return -0 for rounding to -infinity
v.result_sign := r.round_mode(1) and r.round_mode(0);
arith_done := '1';
elsif r.a.class = INFINITY or r.b.class = ZERO then
-- nothing to do, result is A
-- result is A
v.opsel_a := AIN_A;
v.state := EXC_RESULT;
else
-- result is +/- B
v.result_sign := r.b.negative xnor r.insn(1);
v.result_class := r.b.class;
v.result_exp := r.b.exponent;
opsel_a <= AIN_B;
v.opsel_a := AIN_B;
v.negate := not r.insn(1);
v.state := EXC_RESULT;
end if;
arith_done := '1';
end if;

when DO_FMUL =>
-- fmul[s]
opsel_a <= AIN_A;
v.result_sign := r.a.negative;
-- r.opsel_a = AIN_A unless C is denorm and A isn't
v.result_sign := r.a.negative xor r.c.negative;
v.result_class := r.a.class;
v.result_exp := r.a.exponent;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
v.use_a := '1';
v.use_c := '1';
if r.a.class = FINITE and r.c.class = FINITE then
v.result_sign := r.a.negative xor r.c.negative;
v.result_exp := r.a.exponent + r.c.exponent;
-- Renormalize denorm operands
if r.a.mantissa(54) = '0' then
v.state := RENORM_A;
elsif r.c.mantissa(54) = '0' then
opsel_a <= AIN_C;
v.state := RENORM_C;
else
f_to_multiply.valid <= '1';
v.state := MULT_1;
end if;
else
if (r.a.class = NAN and r.a.mantissa(53) = '0') or
(r.c.class = NAN and r.c.mantissa(53) = '0') then
-- Signalling NAN
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
if r.a.class = NAN then
-- result is A
elsif r.c.class = NAN then
v.result_class := NAN;
v.result_sign := r.c.negative;
opsel_a <= AIN_C;
if r.a.class = NAN or r.c.class = NAN then
v.state := NAN_RESULT;
elsif (r.a.class = INFINITY and r.c.class = ZERO) or
(r.a.class = ZERO and r.c.class = INFINITY) then
-- invalid operation, construct QNaN
@ -1247,22 +1263,22 @@ begin
qnan_result := '1';
elsif r.a.class = ZERO or r.a.class = INFINITY then
-- result is +/- A
v.result_sign := r.a.negative xor r.c.negative;
arith_done := '1';
else
-- r.c.class is ZERO or INFINITY
v.result_class := r.c.class;
v.result_sign := r.a.negative xor r.c.negative;
v.opsel_a := AIN_C;
v.negate := r.a.negative;
v.state := EXC_RESULT;
end if;
arith_done := '1';
end if;

when DO_FDIV =>
opsel_a <= AIN_A;
v.result_sign := r.a.negative;
-- r.opsel_a = AIN_A unless B is denorm and A isn't
v.result_class := r.a.class;
v.result_exp := r.a.exponent;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
v.use_a := '1';
v.use_b := '1';
v.result_sign := r.a.negative xor r.b.negative;
v.result_exp := r.a.exponent - r.b.exponent;
v.count := "00";
@ -1271,26 +1287,14 @@ begin
if r.a.mantissa(54) = '0' then
v.state := RENORM_A;
elsif r.b.mantissa(54) = '0' then
opsel_a <= AIN_B;
v.state := RENORM_B;
else
v.first := '1';
v.state := DIV_2;
end if;
else
if (r.a.class = NAN and r.a.mantissa(53) = '0') or
(r.b.class = NAN and r.b.mantissa(53) = '0') then
-- Signalling NAN
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
if r.a.class = NAN then
-- result is A
v.result_sign := r.a.negative;
elsif r.b.class = NAN then
v.result_class := NAN;
v.result_sign := r.b.negative;
opsel_a <= AIN_B;
if r.a.class = NAN or r.b.class = NAN then
v.state := NAN_RESULT;
elsif r.b.class = INFINITY then
if r.a.class = INFINITY then
v.fpscr(FPSCR_VXIDI) := '1';
@ -1298,6 +1302,7 @@ begin
else
v.result_class := ZERO;
end if;
arith_done := '1';
elsif r.b.class = ZERO then
if r.a.class = ZERO then
v.fpscr(FPSCR_VXZDZ) := '1';
@ -1308,46 +1313,36 @@ begin
end if;
v.result_class := INFINITY;
end if;
-- else r.b.class = FINITE, result_class = r.a.class
end if;
arith_done := '1';
else -- r.b.class = FINITE, result_class = r.a.class
arith_done := '1';
end if;
end if;

when DO_FSEL =>
opsel_a <= AIN_A;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
if r.a.class = ZERO or (r.a.negative = '0' and r.a.class /= NAN) then
v.result_sign := r.c.negative;
v.result_exp := r.c.exponent;
v.result_class := r.c.class;
opsel_a <= AIN_C;
v.opsel_a := AIN_C;
else
v.result_sign := r.b.negative;
v.result_exp := r.b.exponent;
v.result_class := r.b.class;
opsel_a <= AIN_B;
v.opsel_a := AIN_B;
end if;
v.quieten_nan := '0';
arith_done := '1';
v.state := EXC_RESULT;

when DO_FSQRT =>
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B
v.result_class := r.b.class;
v.result_sign := r.b.negative;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
if r.b.class = NAN and r.b.mantissa(53) = '0' then
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
v.use_b := '1';
case r.b.class is
when FINITE =>
v.result_exp := r.b.exponent;
if r.b.negative = '1' then
v.fpscr(FPSCR_VXSQRT) := '1';
qnan_result := '1';
arith_done := '1';
elsif r.b.mantissa(54) = '0' then
v.state := RENORM_B;
elsif r.b.exponent(0) = '0' then
@ -1356,7 +1351,9 @@ begin
v.shift := to_signed(1, EXP_BITS);
v.state := RENORM_B2;
end if;
when NAN | ZERO =>
when NAN =>
v.state := NAN_RESULT;
when ZERO =>
-- result is B
arith_done := '1';
when INFINITY =>
@ -1369,15 +1366,12 @@ begin
end case;

when DO_FRE =>
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B
v.result_class := r.b.class;
v.result_sign := r.b.negative;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
if r.b.class = NAN and r.b.mantissa(53) = '0' then
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
v.use_b := '1';
case r.b.class is
when FINITE =>
v.result_exp := - r.b.exponent;
@ -1387,8 +1381,7 @@ begin
v.state := FRE_1;
end if;
when NAN =>
-- result is B
arith_done := '1';
v.state := NAN_RESULT;
when INFINITY =>
v.result_class := ZERO;
arith_done := '1';
@ -1399,15 +1392,12 @@ begin
end case;

when DO_FRSQRTE =>
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B
v.result_class := r.b.class;
v.result_sign := r.b.negative;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
if r.b.class = NAN and r.b.mantissa(53) = '0' then
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
v.use_b := '1';
v.shift := to_signed(1, EXP_BITS);
case r.b.class is
when FINITE =>
@ -1415,7 +1405,6 @@ begin
if r.b.negative = '1' then
v.fpscr(FPSCR_VXSQRT) := '1';
qnan_result := '1';
arith_done := '1';
elsif r.b.mantissa(54) = '0' then
v.state := RENORM_B;
elsif r.b.exponent(0) = '0' then
@ -1424,8 +1413,7 @@ begin
v.state := RENORM_B2;
end if;
when NAN =>
-- result is B
arith_done := '1';
v.state := NAN_RESULT;
when INFINITY =>
if r.b.negative = '1' then
v.fpscr(FPSCR_VXSQRT) := '1';
@ -1442,25 +1430,26 @@ begin

when DO_FMADD =>
-- fmadd, fmsub, fnmadd, fnmsub
opsel_a <= AIN_A;
-- r.opsel_a = AIN_A if A is denorm, else AIN_C if C is denorm,
-- else AIN_B
v.result_sign := r.a.negative;
v.result_class := r.a.class;
v.result_exp := r.a.exponent;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
v.use_a := '1';
v.use_b := '1';
v.use_c := '1';
is_add := r.a.negative xor r.c.negative xor r.b.negative xor r.insn(1);
if r.a.class = FINITE and r.c.class = FINITE and
(r.b.class = FINITE or r.b.class = ZERO) then
v.is_subtract := not is_add;
mulexp := r.a.exponent + r.c.exponent;
v.result_exp := mulexp;
opsel_a <= AIN_B;
-- Make sure A and C are normalized
if r.a.mantissa(54) = '0' then
opsel_a <= AIN_A;
v.state := RENORM_A;
elsif r.c.mantissa(54) = '0' then
opsel_a <= AIN_C;
v.state := RENORM_C;
elsif r.b.class = ZERO then
-- no addend, degenerates to multiply
@ -1483,25 +1472,8 @@ begin
v.state := FMADD_2;
end if;
else
if (r.a.class = NAN and r.a.mantissa(53) = '0') or
(r.b.class = NAN and r.b.mantissa(53) = '0') or
(r.c.class = NAN and r.c.mantissa(53) = '0') then
-- Signalling NAN
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
if r.a.class = NAN then
-- nothing to do, result is A
elsif r.b.class = NAN then
-- result is B
v.result_class := NAN;
v.result_sign := r.b.negative;
opsel_a <= AIN_B;
elsif r.c.class = NAN then
-- result is C
v.result_class := NAN;
v.result_sign := r.c.negative;
opsel_a <= AIN_C;
if r.a.class = NAN or r.b.class = NAN or r.c.class = NAN then
v.state := NAN_RESULT;
elsif (r.a.class = ZERO and r.c.class = INFINITY) or
(r.a.class = INFINITY and r.c.class = ZERO) then
-- invalid operation, construct QNaN
@ -1516,32 +1488,36 @@ begin
-- result is infinity
v.result_class := INFINITY;
v.result_sign := r.a.negative xor r.c.negative xor r.insn(2);
arith_done := '1';
end if;
else
-- Here A is zero, C is zero, or B is infinity
-- Result is +/-B in all of those cases
v.result_class := r.b.class;
v.result_exp := r.b.exponent;
if v.result_class /= ZERO or is_add = '1' then
v.result_sign := not (r.b.negative xor r.insn(1) xor r.insn(2));
v.opsel_a := AIN_B;
if r.b.class /= ZERO or is_add = '1' then
v.negate := not (r.insn(1) xor r.insn(2));
else
-- have to be careful about rule for 0 - 0 result sign
v.result_sign := (r.round_mode(1) and r.round_mode(0)) xor r.insn(2);
v.negate := r.b.negative xor (r.round_mode(1) and r.round_mode(0)) xor r.insn(2);
end if;
opsel_a <= AIN_B;
v.state := EXC_RESULT;
end if;
arith_done := '1';
end if;

when RENORM_A =>
renormalize := '1';
v.state := RENORM_A2;
if r.insn(4) = '1' then
v.opsel_a := AIN_C;
else
v.opsel_a := AIN_B;
end if;

when RENORM_A2 =>
-- r.opsel_a = AIN_C for fmul/fmadd, AIN_B for fdiv
set_a := '1';
v.result_exp := new_exp;
if r.insn(4) = '1' then
opsel_a <= AIN_C;
if r.c.mantissa(54) = '1' then
if r.insn(3) = '0' or r.b.class = ZERO then
v.first := '1';
@ -1551,13 +1527,13 @@ begin
if new_exp + 1 >= r.b.exponent then
v.madd_cmp := '1';
end if;
v.opsel_a := AIN_B;
v.state := DO_FMADD;
end if;
else
v.state := RENORM_C;
end if;
else
opsel_a <= AIN_B;
if r.b.mantissa(54) = '1' then
v.first := '1';
v.state := DIV_2;
@ -1578,6 +1554,7 @@ begin
else
v.result_exp := new_exp;
end if;
v.opsel_a := AIN_B;
v.state := LOOKUP;

when RENORM_C =>
@ -1595,23 +1572,31 @@ begin
if new_exp + 1 >= r.b.exponent then
v.madd_cmp := '1';
end if;
v.opsel_a := AIN_B;
v.state := DO_FMADD;
end if;

when ADD_1 =>
-- transferring B to R
v.shift := r.b.exponent - r.a.exponent;
v.result_exp := r.b.exponent;
v.state := ADD_SHIFT;

when ADD_SHIFT =>
-- r.shift = - exponent difference
opsel_r <= RES_SHIFT;
v.x := s_nz;
set_x := '1';
longmask := '0';
v.state := ADD_2;

when ADD_2 =>
if r.add_bsmall = '1' then
opsel_a <= AIN_A;
v.opsel_a := AIN_A;
else
opsel_a <= AIN_B;
v.opsel_a := AIN_B;
end if;
v.state := ADD_2;

when ADD_2 =>
-- r.opsel_a = AIN_A if r.add_bsmall = 1 else AIN_B
opsel_b <= BIN_R;
opsel_binv <= r.is_subtract;
carry_in <= r.is_subtract and not r.x;
@ -1655,7 +1640,7 @@ begin
end if;

when CMP_1 =>
opsel_a <= AIN_A;
-- r.opsel_a = AIN_A
opsel_b <= BIN_R;
opsel_binv <= '1';
carry_in <= '1';
@ -1696,7 +1681,7 @@ begin

when FMADD_2 =>
-- Product is potentially bigger here
-- r.shift = addend exp - product exp + 64
-- r.shift = addend exp - product exp + 64, r.r = r.b.mantissa
set_s := '1';
opsel_s <= S_SHIFT;
v.shift := r.shift - to_signed(64, EXP_BITS);
@ -1757,7 +1742,7 @@ begin
end if;

when LOOKUP =>
opsel_a <= AIN_B;
-- r.opsel_a = AIN_B
-- wait one cycle for inverse_table[B] lookup
v.first := '1';
if r.insn(4) = '0' then
@ -2260,6 +2245,41 @@ begin
opsel_r <= RES_SHIFT;
arith_done := '1';

when NAN_RESULT =>
if (r.use_a = '1' and r.a.class = NAN and r.a.mantissa(53) = '0') or
(r.use_b = '1' and r.b.class = NAN and r.b.mantissa(53) = '0') or
(r.use_c = '1' and r.c.class = NAN and r.c.mantissa(53) = '0') then
-- Signalling NAN
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
if r.use_a = '1' and r.a.class = NAN then
v.opsel_a := AIN_A;
elsif r.use_b = '1' and r.b.class = NAN then
v.opsel_a := AIN_B;
elsif r.use_c = '1' and r.c.class = NAN then
v.opsel_a := AIN_C;
end if;
v.state := EXC_RESULT;

when EXC_RESULT =>
-- r.opsel_a = AIN_A, AIN_B or AIN_C according to which input is the result
case r.opsel_a is
when AIN_B =>
v.result_sign := r.b.negative xor r.negate;
v.result_exp := r.b.exponent;
v.result_class := r.b.class;
when AIN_C =>
v.result_sign := r.c.negative xor r.negate;
v.result_exp := r.c.exponent;
v.result_class := r.c.class;
when others =>
v.result_sign := r.a.negative xor r.negate;
v.result_exp := r.a.exponent;
v.result_class := r.a.class;
end case;
arith_done := '1';

end case;

if zero_divide = '1' then
@ -2271,11 +2291,15 @@ begin
v.result_sign := '0';
misc_sel <= "0001";
opsel_r <= RES_MISC;
arith_done := '1';
end if;
if invalid = '1' then
v.invalid := '1';
end if;
if arith_done = '1' then
-- Enabled invalid exception doesn't write result or FPRF
-- Neither does enabled zero-divide exception
if (invalid and r.fpscr(FPSCR_VE)) = '0' and
if (v.invalid and r.fpscr(FPSCR_VE)) = '0' and
(zero_divide and r.fpscr(FPSCR_ZE)) = '0' then
v.writing_back := '1';
v.update_fprf := '1';
@ -2355,7 +2379,7 @@ begin
else
mask := right_mask(unsigned(mshift(5 downto 0)));
end if;
case opsel_a is
case r.opsel_a is
when AIN_R =>
in_a0 := r.r;
when AIN_A =>

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