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FPU: Implement fmul[s]

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This implements the fmul and fmuls instructions.

For fmul[s] with denormalized operands we normalize the inputs
before doing the multiplication, to eliminate the need for doing
count-leading-zeroes on P.  This adds 3 or 5 cycles to the
execution time when one or both operands are denormalized.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras
2020-07-27 18:27:50 +10:00
parent 86b826cd7e
commit e6a5f237bc
7 changed files with 271 additions and 4 deletions
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2
decode1.vhdl
View File

@@ -418,6 +418,7 @@ architecture behaviour of decode1 is
2#01110# => (FPU, OP_FPOP_I, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fcfid[u]s
2#10100# => (FPU, OP_FPOP, FRA, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fsubs
2#10101# => (FPU, OP_FPOP, FRA, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fadds
2#11001# => (FPU, OP_FPOP, FRA, NONE, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fmuls
others => illegal_inst
);
@@ -470,6 +471,7 @@ architecture behaviour of decode1 is
-- op in out A out in out len ext pipe
2#0100# => (FPU, OP_FPOP, FRA, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fsub
2#0101# => (FPU, OP_FPOP, FRA, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fadd
2#1001# => (FPU, OP_FPOP, FRA, NONE, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fmul
others => illegal_inst
);

7
decode2.vhdl
View File

@@ -152,6 +152,12 @@ architecture behaviour of decode2 is
else
return ('0', (others => '0'), (others => '0'));
end if;
when FRC =>
if HAS_FPU then
return ('1', fpr_to_gspr(insn_frc(insn_in)), reg_data);
else
return ('0', (others => '0'), (others => '0'));
end if;
when NONE =>
return ('0', (others => '0'), (others => '0'));
end case;
@@ -308,6 +314,7 @@ begin
else fpr_to_gspr(insn_frb(d_in.insn)) when d_in.decode.input_reg_b = FRB and HAS_FPU
else gpr_to_gspr(insn_rb(d_in.insn));
r_out.read3_reg <= gpr_to_gspr(insn_rcreg(d_in.insn)) when d_in.decode.input_reg_c = RCR
else fpr_to_gspr(insn_frc(d_in.insn)) when d_in.decode.input_reg_c = FRC and HAS_FPU
else fpr_to_gspr(insn_frt(d_in.insn)) when d_in.decode.input_reg_c = FRS and HAS_FPU
else gpr_to_gspr(insn_rs(d_in.insn));

2
decode_types.vhdl
View File

@@ -26,7 +26,7 @@ package decode_types is
type input_reg_a_t is (NONE, RA, RA_OR_ZERO, SPR, CIA, FRA);
type input_reg_b_t is (NONE, RB, CONST_UI, CONST_SI, CONST_SI_HI, CONST_UI_HI, CONST_LI, CONST_BD,
CONST_DXHI4, CONST_DS, CONST_M1, CONST_SH, CONST_SH32, SPR, FRB);
type input_reg_c_t is (NONE, RS, RCR, FRS);
type input_reg_c_t is (NONE, RS, RCR, FRC, FRS);
type output_reg_a_t is (NONE, RT, RA, SPR, FRT);
type rc_t is (NONE, ONE, RC);
type carry_in_t is (ZERO, CA, OV, ONE);

182
fpu.vhdl
View File

@@ -40,15 +40,18 @@ architecture behaviour of fpu is
DO_FMR, DO_FMRG,
DO_FCFID, DO_FCTI,
DO_FRSP, DO_FRI,
DO_FADD,
DO_FADD, DO_FMUL,
FRI_1,
ADD_SHIFT, ADD_2, ADD_3,
MULT_1,
INT_SHIFT, INT_ROUND, INT_ISHIFT,
INT_FINAL, INT_CHECK, INT_OFLOW,
FINISH, NORMALIZE,
ROUND_UFLOW, ROUND_OFLOW,
ROUNDING, ROUNDING_2, ROUNDING_3,
DENORM);
DENORM,
RENORM_A, RENORM_A2,
RENORM_C, RENORM_C2);
type reg_type is record
state : state_t;
@@ -65,8 +68,10 @@ architecture behaviour of fpu is
fpscr : std_ulogic_vector(31 downto 0);
a : fpu_reg_type;
b : fpu_reg_type;
c : fpu_reg_type;
r : std_ulogic_vector(63 downto 0); -- 10.54 format
x : std_ulogic;
p : std_ulogic_vector(63 downto 0); -- 8.56 format
result_sign : std_ulogic;
result_class : fp_number_class;
result_exp : signed(EXP_BITS-1 downto 0);
@@ -84,6 +89,8 @@ architecture behaviour of fpu is
is_subtract : std_ulogic;
exp_cmp : std_ulogic;
add_bsmall : std_ulogic;
is_multiply : std_ulogic;
first : std_ulogic;
end record;
signal r, rin : reg_type;
@@ -103,11 +110,17 @@ architecture behaviour of fpu is
signal r_hi_nz : std_ulogic;
signal r_lo_nz : std_ulogic;
signal misc_sel : std_ulogic_vector(3 downto 0);
signal f_to_multiply : MultiplyInputType;
signal multiply_to_f : MultiplyOutputType;
signal msel_1 : std_ulogic_vector(1 downto 0);
signal msel_2 : std_ulogic_vector(1 downto 0);
signal msel_inv : std_ulogic;
-- opsel values
constant AIN_R : std_ulogic_vector(1 downto 0) := "00";
constant AIN_A : std_ulogic_vector(1 downto 0) := "01";
constant AIN_B : std_ulogic_vector(1 downto 0) := "10";
constant AIN_C : std_ulogic_vector(1 downto 0) := "11";
constant BIN_ZERO : std_ulogic_vector(1 downto 0) := "00";
constant BIN_R : std_ulogic_vector(1 downto 0) := "01";
@@ -115,8 +128,17 @@ architecture behaviour of fpu is
constant RES_SUM : std_ulogic_vector(1 downto 0) := "00";
constant RES_SHIFT : std_ulogic_vector(1 downto 0) := "01";
constant RES_MULT : std_ulogic_vector(1 downto 0) := "10";
constant RES_MISC : std_ulogic_vector(1 downto 0) := "11";
-- msel values
constant MUL1_A : std_ulogic_vector(1 downto 0) := "00";
constant MUL1_B : std_ulogic_vector(1 downto 0) := "01";
constant MUL1_R : std_ulogic_vector(1 downto 0) := "11";
constant MUL2_C : std_ulogic_vector(1 downto 0) := "00";
constant MUL2_R : std_ulogic_vector(1 downto 0) := "11";
-- Left and right shifter with 120 bit input and 64 bit output.
-- Shifts inp left by shift bits and returns the upper 64 bits of
-- the result. The shift parameter is interpreted as a signed
@@ -313,6 +335,13 @@ architecture behaviour of fpu is
end;
begin
fpu_multiply_0: entity work.multiply
port map (
clk => clk,
m_in => f_to_multiply,
m_out => multiply_to_f
);
fpu_0: process(clk)
begin
if rising_edge(clk) then
@@ -347,6 +376,7 @@ begin
variable v : reg_type;
variable adec : fpu_reg_type;
variable bdec : fpu_reg_type;
variable cdec : fpu_reg_type;
variable fpscr_mask : std_ulogic_vector(31 downto 0);
variable illegal : std_ulogic;
variable j, k : integer;
@@ -377,6 +407,10 @@ begin
variable is_add : std_ulogic;
variable qnan_result : std_ulogic;
variable longmask : std_ulogic;
variable set_a : std_ulogic;
variable set_c : std_ulogic;
variable px_nz : std_ulogic;
variable maddend : std_ulogic_vector(127 downto 0);
begin
v := r;
illegal := '0';
@@ -407,11 +441,15 @@ begin
v.denorm := '0';
v.round_mode := '0' & r.fpscr(FPSCR_RN+1 downto FPSCR_RN);
v.is_subtract := '0';
v.is_multiply := '0';
v.add_bsmall := '0';
adec := decode_dp(e_in.fra, int_input);
bdec := decode_dp(e_in.frb, int_input);
cdec := decode_dp(e_in.frc, int_input);
v.a := adec;
v.b := bdec;
v.c := cdec;
v.exp_cmp := '0';
if adec.exponent > bdec.exponent then
v.exp_cmp := '1';
@@ -440,10 +478,14 @@ begin
exp_huge := '1';
end if;
-- Compare P with zero
px_nz := or (r.p(57 downto 4));
v.writing_back := '0';
v.instr_done := '0';
v.update_fprf := '0';
v.shift := to_signed(0, EXP_BITS);
v.first := '0';
opsel_a <= AIN_R;
opsel_ainv <= '0';
opsel_amask <= '0';
@@ -460,6 +502,13 @@ begin
set_x := '0';
qnan_result := '0';
longmask := r.single_prec;
set_a := '0';
set_c := '0';
f_to_multiply.is_32bit <= '0';
f_to_multiply.valid <= '0';
msel_1 <= MUL1_A;
msel_2 <= MUL2_C;
msel_inv <= '0';
case r.state is
when IDLE =>
@@ -503,6 +552,9 @@ begin
v.state := DO_FCTI;
when "10100" | "10101" =>
v.state := DO_FADD;
when "11001" =>
v.is_multiply := '1';
v.state := DO_FMUL;
when others =>
illegal := '1';
end case;
@@ -795,6 +847,81 @@ begin
arith_done := '1';
end if;
when DO_FMUL =>
-- fmul[s]
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';
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;
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
v.fpscr(FPSCR_VXIMZ) := '1';
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;
else
-- r.c.class is ZERO or INFINITY
v.result_class := r.c.class;
v.result_sign := r.a.negative xor r.c.negative;
end if;
arith_done := '1';
end if;
when RENORM_A =>
renormalize := '1';
v.state := RENORM_A2;
when RENORM_A2 =>
set_a := '1';
v.result_exp := new_exp;
opsel_a <= AIN_C;
if r.c.mantissa(54) = '1' then
v.first := '1';
v.state := MULT_1;
else
v.state := RENORM_C;
end if;
when RENORM_C =>
renormalize := '1';
v.state := RENORM_C2;
when RENORM_C2 =>
set_c := '1';
v.result_exp := new_exp;
v.first := '1';
v.state := MULT_1;
when ADD_SHIFT =>
opsel_r <= RES_SHIFT;
set_x := '1';
@@ -848,6 +975,13 @@ begin
v.state := NORMALIZE;
end if;
when MULT_1 =>
f_to_multiply.valid <= r.first;
opsel_r <= RES_MULT;
if multiply_to_f.valid = '1' then
v.state := FINISH;
end if;
when INT_SHIFT =>
opsel_r <= RES_SHIFT;
set_x := '1';
@@ -930,6 +1064,9 @@ begin
v.state := ROUNDING;
when FINISH =>
if r.is_multiply = '1' and px_nz = '1' then
v.x := '1';
end if;
if r.r(63 downto 54) /= "0000000001" then
renormalize := '1';
v.state := NORMALIZE;
@@ -1099,6 +1236,32 @@ begin
update_fx := '1';
end if;
-- Multiplier data path
case msel_1 is
when MUL1_A =>
f_to_multiply.data1 <= r.a.mantissa(61 downto 0) & "00";
when MUL1_B =>
f_to_multiply.data1 <= r.b.mantissa(61 downto 0) & "00";
when others =>
f_to_multiply.data1 <= r.r(61 downto 0) & "00";
end case;
case msel_2 is
when MUL2_C =>
f_to_multiply.data2 <= r.c.mantissa(61 downto 0) & "00";
when others =>
f_to_multiply.data2 <= r.r(61 downto 0) & "00";
end case;
maddend := (others => '0');
if msel_inv = '1' then
f_to_multiply.addend <= not maddend;
else
f_to_multiply.addend <= maddend;
end if;
f_to_multiply.not_result <= msel_inv;
if multiply_to_f.valid = '1' then
v.p := multiply_to_f.result(63 downto 0);
end if;
-- Data path.
-- This has A and B input multiplexers, an adder, a shifter,
-- count-leading-zeroes logic, and a result mux.
@@ -1119,8 +1282,10 @@ begin
in_a0 := r.r;
when AIN_A =>
in_a0 := r.a.mantissa;
when others =>
when AIN_B =>
in_a0 := r.b.mantissa;
when others =>
in_a0 := r.c.mantissa;
end case;
if (or (mask and in_a0)) = '1' and set_x = '1' then
v.x := '1';
@@ -1157,6 +1322,8 @@ begin
result <= std_ulogic_vector(unsigned(in_a) + unsigned(in_b) + carry_in);
when RES_SHIFT =>
result <= shift_res;
when RES_MULT =>
result <= multiply_to_f.result(121 downto 58);
when others =>
case misc_sel is
when "0000" =>
@@ -1207,6 +1374,15 @@ begin
end case;
v.r := result;
if set_a = '1' then
v.a.exponent := new_exp;
v.a.mantissa := shift_res;
end if;
if set_c = '1' then
v.c.exponent := new_exp;
v.c.mantissa := shift_res;
end if;
if opsel_r = RES_SHIFT then
v.result_exp := new_exp;
end if;

80
tests/fpu/fpu.c
View File

@@ -205,6 +205,7 @@ struct sp_dp_equiv {
{ 0x00200000, 0x37f0000000000000 },
{ 0x00000002, 0x36b0000000000000 },
{ 0x00000001, 0x36a0000000000000 },
{ 0x7f7fffff, 0x47efffffe0000000 },
};
int sp_to_dp(long arg)
@@ -995,6 +996,83 @@ int fpu_test_14(void)
return trapit(0, test14);
}
struct mulvals {
unsigned long val_a;
unsigned long val_b;
unsigned long prod;
} mulvals[] = {
{ 0x0000000000000000, 0x0000000000000000, 0x0000000000000000 },
{ 0x8000000000000000, 0x8000000000000000, 0x0000000000000000 },
{ 0x3ff0000000000000, 0x3ff0000000000000, 0x3ff0000000000000 },
{ 0xbff0000000000000, 0x3ff0000000000000, 0xbff0000000000000 },
{ 0xbf4fff801fffffff, 0x6d7fffff8000007f, 0xecdfff7fa001fffe },
{ 0x3fbd50275a65ed80, 0x0010000000000000, 0x0001d50275a65ed8 },
};
int test15(long arg)
{
long i;
unsigned long result;
struct mulvals *vp = mulvals;
set_fpscr(FPS_RN_NEAR);
for (i = 0; i < sizeof(mulvals) / sizeof(mulvals[0]); ++i, ++vp) {
asm("lfd 5,0(%0); lfd 6,8(%0); fmul 7,5,6; stfd 7,0(%1)"
: : "b" (&vp->val_a), "b" (&result) : "memory");
if (result != vp->prod) {
print_hex(i, 2, " ");
print_hex(result, 16, " ");
return i + 1;
}
}
return 0;
}
int fpu_test_15(void)
{
enable_fp();
return trapit(0, test15);
}
struct mulvals_sp {
unsigned int val_a;
unsigned int val_b;
unsigned int prod;
} mulvals_sp[] = {
{ 0x00000000, 0x00000000, 0x00000000 },
{ 0x80000000, 0x80000000, 0x00000000 },
{ 0x3f800000, 0x3f800000, 0x3f800000 },
{ 0xbf800000, 0x3f800000, 0xbf800000 },
{ 0xbe7ff801, 0x6d7fffff, 0xec7ff800 },
{ 0xc100003d, 0xfe803ff8, 0x7f800000 },
{ 0x4f780080, 0x389003ff, 0x488b8427 },
};
int test16(long arg)
{
long i;
unsigned int result;
struct mulvals_sp *vp = mulvals_sp;
set_fpscr(FPS_RN_NEAR);
for (i = 0; i < sizeof(mulvals_sp) / sizeof(mulvals_sp[0]); ++i, ++vp) {
asm("lfs 5,0(%0); lfs 6,4(%0); fmuls 7,5,6; stfs 7,0(%1)"
: : "b" (&vp->val_a), "b" (&result) : "memory");
if (result != vp->prod) {
print_hex(i, 2, " ");
print_hex(result, 8, " ");
return i + 1;
}
}
return 0;
}
int fpu_test_16(void)
{
enable_fp();
return trapit(0, test16);
}
int fail = 0;
void do_test(int num, int (*test)(void))
@@ -1034,6 +1112,8 @@ int main(void)
do_test(12, fpu_test_12);
do_test(13, fpu_test_13);
do_test(14, fpu_test_14);
do_test(15, fpu_test_15);
do_test(16, fpu_test_16);
return fail;
}

BIN
tests/test_fpu.bin
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Binary file not shown.

2
tests/test_fpu.console_out
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@@ -12,3 +12,5 @@ test 11:PASS
test 12:PASS
test 13:PASS
test 14:PASS
test 15:PASS
test 16:PASS