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FPU: Implement the frsp instruction

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This brings in the invalid exception for the case of frsp with a
signalling NaN as input, and the need to be able to convert a
signalling NaN to a quiet NaN.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras
2020-08-31 17:26:33 +10:00
parent 9e8fb293ed
commit 34b5d4a7b5
2 changed files with 45 additions and 5 deletions
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1
decode1.vhdl
View File

@@ -441,6 +441,7 @@ architecture behaviour of decode1 is
2#100000010# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- 2/8=fmr
2#100000100# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- 4/8=fnabs
2#100001000# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- 8/8=fabs
2#110000000# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- 0/12=frsp
2#111011010# => (FPU, OP_FPOP_I, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- 26/14=fcfid
2#111011110# => (FPU, OP_FPOP_I, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- 30/14=fcfidu
others => illegal_inst

49
fpu.vhdl
View File

@@ -39,6 +39,7 @@ architecture behaviour of fpu is
DO_MCRFS, DO_MTFSB, DO_MTFSFI, DO_MFFS, DO_MTFSF,
DO_FMR,
DO_FCFID,
DO_FRSP,
FINISH, NORMALIZE,
ROUND_UFLOW, ROUND_OFLOW,
ROUNDING, ROUNDING_2, ROUNDING_3,
@@ -71,6 +72,7 @@ architecture behaviour of fpu is
cr_mask : std_ulogic_vector(7 downto 0);
old_exc : std_ulogic_vector(4 downto 0);
update_fprf : std_ulogic;
quieten_nan : std_ulogic;
tiny : std_ulogic;
denorm : std_ulogic;
round_mode : std_ulogic_vector(2 downto 0);
@@ -217,7 +219,7 @@ architecture behaviour of fpu is
-- Construct a DP floating-point result from components
function pack_dp(sign: std_ulogic; class: fp_number_class; exp: signed(EXP_BITS-1 downto 0);
mantissa: std_ulogic_vector; single_prec: std_ulogic)
mantissa: std_ulogic_vector; single_prec: std_ulogic; quieten_nan: std_ulogic)
return std_ulogic_vector is
variable result : std_ulogic_vector(63 downto 0);
begin
@@ -238,7 +240,8 @@ architecture behaviour of fpu is
result(62 downto 52) := "11111111111";
when NAN =>
result(62 downto 52) := "11111111111";
result(51 downto 29) := mantissa(53 downto 31);
result(51) := quieten_nan or mantissa(53);
result(50 downto 29) := mantissa(52 downto 31);
if single_prec = '0' then
result(28 downto 0) := mantissa(30 downto 2);
end if;
@@ -348,6 +351,7 @@ begin
variable round : std_ulogic_vector(1 downto 0);
variable update_fx : std_ulogic;
variable arith_done : std_ulogic;
variable invalid : std_ulogic;
variable mant_nz : std_ulogic;
variable min_exp : signed(EXP_BITS-1 downto 0);
variable max_exp : signed(EXP_BITS-1 downto 0);
@@ -384,6 +388,7 @@ begin
if e_in.op = OP_FPOP_I then
int_input := '1';
end if;
v.quieten_nan := '1';
v.tiny := '0';
v.denorm := '0';
v.round_mode := '0' & r.fpscr(FPSCR_RN+1 downto FPSCR_RN);
@@ -429,6 +434,7 @@ begin
fpscr_mask := (others => '1');
update_fx := '0';
arith_done := '0';
invalid := '0';
renormalize := '0';
set_x := '0';
@@ -452,6 +458,8 @@ begin
end if;
when "01000" =>
v.state := DO_FMR;
when "01100" =>
v.state := DO_FRSP;
when "01110" =>
-- fcfid[u][s]
v.state := DO_FCFID;
@@ -552,6 +560,7 @@ begin
opsel_a <= AIN_B;
v.result_class := r.b.class;
v.result_exp := r.b.exponent;
v.quieten_nan := '0';
if r.insn(9) = '1' then
v.result_sign := '0'; -- fabs
elsif r.insn(8) = '1' then
@@ -567,6 +576,33 @@ begin
v.instr_done := '1';
v.state := IDLE;
when DO_FRSP =>
opsel_a <= AIN_B;
v.result_class := r.b.class;
v.result_sign := r.b.negative;
v.result_exp := r.b.exponent;
v.fpscr(FPSCR_FR) := '0';
v.fpscr(FPSCR_FI) := '0';
if r.b.class = NAN and r.b.mantissa(53) = '0' then
-- Signalling NAN
v.fpscr(FPSCR_VXSNAN) := '1';
invalid := '1';
end if;
set_x := '1';
if r.b.class = FINITE then
if r.b.exponent < to_signed(-126, EXP_BITS) then
v.shift := r.b.exponent - to_signed(-126, EXP_BITS);
v.state := ROUND_UFLOW;
elsif r.b.exponent > to_signed(127, EXP_BITS) then
v.state := ROUND_OFLOW;
else
v.shift := to_signed(-2, EXP_BITS);
v.state := ROUNDING;
end if;
else
arith_done := '1';
end if;
when DO_FCFID =>
v.result_sign := '0';
opsel_a <= AIN_B;
@@ -735,8 +771,11 @@ begin
end case;
if arith_done = '1' then
v.writing_back := '1';
v.update_fprf := '1';
-- Enabled invalid exception doesn't write result or FPRF
if (invalid and r.fpscr(FPSCR_VE)) = '0' then
v.writing_back := '1';
v.update_fprf := '1';
end if;
v.instr_done := '1';
v.state := IDLE;
update_fx := '1';
@@ -827,7 +866,7 @@ begin
fp_result <= r.r;
else
fp_result <= pack_dp(r.result_sign, r.result_class, r.result_exp, r.r,
r.single_prec);
r.single_prec, r.quieten_nan);
end if;
if r.update_fprf = '1' then
v.fpscr(FPSCR_C downto FPSCR_FU) := result_flags(r.result_sign, r.result_class,