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FPU: Implement floating multiply-add instructions

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This implements fmadd, fmsub, fnmadd, fnmsub and their
single-precision counterparts.  The single-precision versions operate
the same as the double-precision versions until the final rounding and
overflow/underflow steps.

This adds an S register to store the low bits of the product.  S
shifts into R on left shifts, and can be negated, but doesn't do any
other arithmetic.

This adds a test for the double-precision versions of these
instructions.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/245/head
Paul Mackerras 4 years ago
parent c083b9507d
commit dc1544db69
5 changed files with 314 additions and 10 deletions
Show Stats Download Patch File Download Diff File

8
decode1.vhdl
Unescape Escape View File

@ -423,6 +423,10 @@ architecture behaviour of decode1 is
2#11000# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fres
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
2#11010# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- frsqrtes
2#11100# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fmsubs
2#11101# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fmadds
2#11110# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fnmsubs
2#11111# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '0', RC, '0', '0'), -- fnmadds
others => illegal_inst
);

@ -485,6 +489,10 @@ architecture behaviour of decode1 is
2#1000# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fre
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
2#1010# => (FPU, OP_FPOP, NONE, FRB, NONE, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- frsqrte
2#1100# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fmsub
2#1101# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fmadd
2#1110# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fnmsub
2#1111# => (FPU, OP_FPOP, FRA, FRB, FRC, FRT, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC, '0', '0'), -- fnmadd
others => illegal_inst
);


244
fpu.vhdl
Unescape Escape View File

@ -40,13 +40,15 @@ architecture behaviour of fpu is
DO_FMR, DO_FMRG, DO_FCMP, DO_FTDIV, DO_FTSQRT,
DO_FCFID, DO_FCTI,
DO_FRSP, DO_FRI,
DO_FADD, DO_FMUL, DO_FDIV, DO_FSQRT,
DO_FADD, DO_FMUL, DO_FDIV, DO_FSQRT, DO_FMADD,
DO_FRE, DO_FRSQRTE,
DO_FSEL,
FRI_1,
ADD_SHIFT, ADD_2, ADD_3,
CMP_1, CMP_2,
MULT_1,
FMADD_1, FMADD_2, FMADD_3,
FMADD_4, FMADD_5, FMADD_6,
LOOKUP,
DIV_2, DIV_3, DIV_4, DIV_5, DIV_6,
FRE_1,
@ -82,6 +84,7 @@ architecture behaviour of fpu is
b : fpu_reg_type;
c : fpu_reg_type;
r : std_ulogic_vector(63 downto 0); -- 10.54 format
s : std_ulogic_vector(55 downto 0); -- extended fraction
x : std_ulogic;
p : std_ulogic_vector(63 downto 0); -- 8.56 format
y : std_ulogic_vector(63 downto 0); -- 8.56 format
@ -101,6 +104,7 @@ architecture behaviour of fpu is
round_mode : std_ulogic_vector(2 downto 0);
is_subtract : std_ulogic;
exp_cmp : std_ulogic;
madd_cmp : std_ulogic;
add_bsmall : std_ulogic;
is_multiply : std_ulogic;
is_sqrt : std_ulogic;
@ -117,6 +121,7 @@ architecture behaviour of fpu is
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);
signal opsel_ainv : std_ulogic;
signal opsel_amask : std_ulogic;
signal opsel_binv : std_ulogic;
@ -127,6 +132,7 @@ architecture behaviour of fpu is
signal lost_bits : std_ulogic;
signal r_hi_nz : std_ulogic;
signal r_lo_nz : std_ulogic;
signal s_nz : std_ulogic;
signal misc_sel : std_ulogic_vector(3 downto 0);
signal f_to_multiply : MultiplyInputType;
signal multiply_to_f : MultiplyOutputType;
@ -152,6 +158,11 @@ architecture behaviour of fpu is
constant RES_MULT : std_ulogic_vector(1 downto 0) := "10";
constant RES_MISC : std_ulogic_vector(1 downto 0) := "11";

constant S_ZERO : std_ulogic_vector(1 downto 0) := "00";
constant S_NEG : std_ulogic_vector(1 downto 0) := "01";
constant S_SHIFT : std_ulogic_vector(1 downto 0) := "10";
constant S_MULT : 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";
@ -163,9 +174,10 @@ architecture behaviour of fpu is
constant MUL2_P : std_ulogic_vector(1 downto 0) := "10";
constant MUL2_R : std_ulogic_vector(1 downto 0) := "11";

constant MULADD_ZERO : std_ulogic_vector(1 downto 0) := "00";
constant MULADD_ZERO : std_ulogic_vector(1 downto 0) := "00";
constant MULADD_CONST : std_ulogic_vector(1 downto 0) := "01";
constant MULADD_A : std_ulogic_vector(1 downto 0) := "10";
constant MULADD_RS : std_ulogic_vector(1 downto 0) := "11";

-- Inverse lookup table, indexed by the top 8 fraction bits
-- The first 256 entries are the reciprocal (1/x) lookup table,
@ -597,20 +609,22 @@ begin
variable need_check : std_ulogic;
variable msb : std_ulogic;
variable is_add : std_ulogic;
variable qnan_result : std_ulogic;
variable longmask : std_ulogic;
variable set_a : std_ulogic;
variable set_b : std_ulogic;
variable set_c : std_ulogic;
variable px_nz : std_ulogic;
variable maddend : std_ulogic_vector(127 downto 0);
variable set_y : std_ulogic;
variable set_s : std_ulogic;
variable qnan_result : std_ulogic;
variable px_nz : std_ulogic;
variable pcmpb_eq : std_ulogic;
variable pcmpb_lt : std_ulogic;
variable pshift : std_ulogic;
variable renorm_sqrt : std_ulogic;
variable sqrt_exp : signed(EXP_BITS-1 downto 0);
variable shiftin : std_ulogic;
variable mulexp : signed(EXP_BITS-1 downto 0);
variable maddend : std_ulogic_vector(127 downto 0);
begin
v := r;
illegal := '0';
@ -657,10 +671,15 @@ begin
if adec.exponent > bdec.exponent then
v.exp_cmp := '1';
end if;
v.madd_cmp := '0';
if (adec.exponent + cdec.exponent + 1) >= bdec.exponent then
v.madd_cmp := '1';
end if;
end if;

r_hi_nz <= or (r.r(55 downto 31));
r_lo_nz <= or (r.r(30 downto 2));
s_nz <= or (r.s);

if r.single_prec = '0' then
if r.doing_ftdiv(1) = '0' then
@ -711,6 +730,7 @@ begin
opsel_b <= BIN_ZERO;
opsel_binv <= '0';
opsel_r <= RES_SUM;
opsel_s <= S_ZERO;
carry_in <= '0';
misc_sel <= "0000";
fpscr_mask := (others => '1');
@ -725,6 +745,7 @@ begin
set_a := '0';
set_b := '0';
set_c := '0';
set_s := '0';
f_to_multiply.is_32bit <= '0';
f_to_multiply.valid <= '0';
msel_1 <= MUL1_A;
@ -802,12 +823,15 @@ begin
when "11010" =>
v.is_sqrt := '1';
v.state := DO_FRSQRTE;
when "11100" | "11101" | "11110" | "11111" =>
v.state := DO_FMADD;
when others =>
illegal := '1';
end case;
end if;
v.x := '0';
v.old_exc := r.fpscr(FPSCR_VX downto FPSCR_XX);
set_s := '1';

when DO_MCRFS =>
j := to_integer(unsigned(insn_bfa(r.insn)));
@ -1416,6 +1440,99 @@ begin
arith_done := '1';
end case;

when DO_FMADD =>
-- fmadd, fmsub, fnmadd, fnmsub
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';
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
v.result_sign := r.a.negative xor r.c.negative xor r.insn(2);
f_to_multiply.valid <= '1';
v.is_multiply := '1';
v.state := MULT_1;
elsif r.madd_cmp = '0' then
-- addend is bigger, do multiply first
v.result_sign := not (r.b.negative xor r.insn(1) xor r.insn(2));
f_to_multiply.valid <= '1';
v.state := FMADD_1;
else
-- product is bigger, shift B right and use it as the
-- addend to the multiplier
v.shift := r.b.exponent - mulexp + to_signed(64, EXP_BITS);
-- for subtract, multiplier does B - A * C
v.result_sign := not (r.a.negative xor r.c.negative xor r.insn(2) xor is_add);
v.result_exp := r.b.exponent;
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;
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
v.fpscr(FPSCR_VXIMZ) := '1';
qnan_result := '1';
elsif r.a.class = INFINITY or r.c.class = INFINITY then
if r.b.class = INFINITY and is_add = '0' then
-- invalid operation, construct QNaN
v.fpscr(FPSCR_VXISI) := '1';
qnan_result := '1';
else
-- result is infinity
v.result_class := INFINITY;
v.result_sign := r.a.negative xor r.c.negative xor r.insn(2);
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));
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);
end if;
opsel_a <= AIN_B;
end if;
arith_done := '1';
end if;

when RENORM_A =>
renormalize := '1';
v.state := RENORM_A2;
@ -1426,8 +1543,16 @@ begin
if r.insn(4) = '1' then
opsel_a <= AIN_C;
if r.c.mantissa(54) = '1' then
v.first := '1';
v.state := MULT_1;
if r.insn(3) = '0' or r.b.class = ZERO then
v.first := '1';
v.state := MULT_1;
else
v.madd_cmp := '0';
if new_exp + 1 >= r.b.exponent then
v.madd_cmp := '1';
end if;
v.state := DO_FMADD;
end if;
else
v.state := RENORM_C;
end if;
@ -1462,11 +1587,20 @@ begin
when RENORM_C2 =>
set_c := '1';
v.result_exp := new_exp;
v.first := '1';
v.state := MULT_1;
if r.insn(3) = '0' or r.b.class = ZERO then
v.first := '1';
v.state := MULT_1;
else
v.madd_cmp := '0';
if new_exp + 1 >= r.b.exponent then
v.madd_cmp := '1';
end if;
v.state := DO_FMADD;
end if;

when ADD_SHIFT =>
opsel_r <= RES_SHIFT;
v.x := s_nz;
set_x := '1';
longmask := '0';
v.state := ADD_2;
@ -1545,6 +1679,78 @@ begin
v.state := FINISH;
end if;

when FMADD_1 =>
-- Addend is bigger here
v.result_sign := not (r.b.negative xor r.insn(1) xor r.insn(2));
-- note v.shift is at most -2 here
v.shift := r.result_exp - r.b.exponent;
opsel_r <= RES_MULT;
opsel_s <= S_MULT;
set_s := '1';
f_to_multiply.valid <= r.first;
if multiply_to_f.valid = '1' then
v.state := ADD_SHIFT;
end if;

when FMADD_2 =>
-- Product is potentially bigger here
set_s := '1';
opsel_s <= S_SHIFT;
v.shift := r.shift - to_signed(64, EXP_BITS);
v.state := FMADD_3;

when FMADD_3 =>
opsel_r <= RES_SHIFT;
v.first := '1';
v.state := FMADD_4;

when FMADD_4 =>
msel_add <= MULADD_RS;
f_to_multiply.valid <= r.first;
msel_inv <= r.is_subtract;
opsel_r <= RES_MULT;
opsel_s <= S_MULT;
set_s := '1';
v.shift := to_signed(56, EXP_BITS);
if multiply_to_f.valid = '1' then
if multiply_to_f.result(121) = '1' then
v.state := FMADD_5;
else
v.state := FMADD_6;
end if;
end if;

when FMADD_5 =>
-- negate R:S:X
v.result_sign := not r.result_sign;
opsel_ainv <= '1';
carry_in <= not (s_nz or r.x);
opsel_s <= S_NEG;
set_s := '1';
v.shift := to_signed(56, EXP_BITS);
v.state := FMADD_6;

when FMADD_6 =>
if (r.r(56) or r_hi_nz or r_lo_nz or r.r(1) or r.r(0)) = '0' then
if s_nz = '0' then
-- must be a subtraction, and r.x must be zero
v.result_class := ZERO;
v.result_sign := r.round_mode(1) and r.round_mode(0);
arith_done := '1';
else
-- R is all zeroes but there are non-zero bits in S
-- so shift them into R and set S to 0
opsel_r <= RES_SHIFT;
set_s := '1';
-- stay in state FMADD_6
end if;
elsif r.r(56 downto 54) = "001" then
v.state := FINISH;
else
renormalize := '1';
v.state := NORMALIZE;
end if;

when LOOKUP =>
opsel_a <= AIN_B;
-- wait one cycle for inverse_table[B] lookup
@ -2097,6 +2303,9 @@ begin
when MULADD_A =>
-- addend is A in 16.112 format
maddend(121 downto 58) := r.a.mantissa;
when MULADD_RS =>
-- addend is concatenation of R and S in 16.112 format
maddend := "000000" & r.r & r.s & "00";
when others =>
end case;
if msel_inv = '1' then
@ -2167,7 +2376,7 @@ begin
end if;
in_b <= in_b0;
if r.shift >= to_signed(-64, EXP_BITS) and r.shift <= to_signed(63, EXP_BITS) then
shift_res := shifter_64(r.r & shiftin & 55x"00000000000000",
shift_res := shifter_64(r.r & (shiftin or r.s(55)) & r.s(54 downto 0),
std_ulogic_vector(r.shift(6 downto 0)));
else
shift_res := (others => '0');
@ -2230,6 +2439,21 @@ begin
result <= misc;
end case;
v.r := result;
if set_s = '1' then
case opsel_s is
when S_NEG =>
v.s := std_ulogic_vector(unsigned(not r.s) + (not r.x));
when S_MULT =>
v.s := multiply_to_f.result(57 downto 2);
when S_SHIFT =>
v.s := shift_res(63 downto 8);
if shift_res(7 downto 0) /= x"00" then
v.x := '1';
end if;
when others =>
v.s := (others => '0');
end case;
end if;

if set_a = '1' then
v.a.exponent := new_exp;

71
tests/fpu/fpu.c
Unescape Escape View File

@ -1338,6 +1338,76 @@ int fpu_test_22(void)
return trapit(0, test22);
}

struct fmavals {
unsigned long ra;
unsigned long rc;
unsigned long rb;
unsigned long fma;
unsigned long fms;
unsigned long nfma;
unsigned long nfms;
} fmavals[] = {
{ 0x0000000000000000, 0x0000000000000000, 0x0000000000000000,
0x0000000000000000, 0x0000000000000000, 0x8000000000000000, 0x8000000000000000 },
{ 0x0000000000000000, 0x7ffc000000000000, 0x0000000000000000,
0x7ffc000000000000, 0x7ffc000000000000, 0x7ffc000000000000, 0x7ffc000000000000 },
{ 0x0000000000000000, 0x7ffc000000000000, 0x7ffb000000000000,
0x7ffb000000000000, 0x7ffb000000000000, 0x7ffb000000000000, 0x7ffb000000000000 },
{ 0x7ffa000000000000, 0x7ffc000000000000, 0x7ffb000000000000,
0x7ffa000000000000, 0x7ffa000000000000, 0x7ffa000000000000, 0x7ffa000000000000 },
{ 0x3ff0000000000000, 0x8000000000000000, 0x678123456789abcd,
0x678123456789abcd, 0xe78123456789abcd, 0xe78123456789abcd, 0x678123456789abcd },
{ 0x3ff0000000000000, 0xbff0000000000000, 0x678123456789abcd,
0x678123456789abcd, 0xe78123456789abcd, 0xe78123456789abcd, 0x678123456789abcd },
{ 0x7ff0000000000000, 0xbff0000000000000, 0x678123456789abcd,
0xfff0000000000000, 0xfff0000000000000, 0x7ff0000000000000, 0x7ff0000000000000 },
{ 0x7ff0000000000000, 0x0000000000000000, 0x678123456789abcd,
0x7ff8000000000000, 0x7ff8000000000000, 0x7ff8000000000000, 0x7ff8000000000000 },
{ 0x3ff0000000000000, 0x3ff0000000000000, 0x3ff0000020000000,
0x4000000010000000, 0xbe80000000000000, 0xc000000010000000, 0x3e80000000000000 },
{ 0x3ff0000000000001, 0x3ff0000000000001, 0x3ff0000000000000,
0x4000000000000001, 0x3cc0000000000000, 0xc000000000000001, 0xbcc0000000000000 },
{ 0x3ff0000000000003, 0x3ff0000000000002, 0x3ff0000000000000,
0x4000000000000002, 0x3cd4000000000002, 0xc000000000000002, 0xbcd4000000000002 },
{ 0x3006a09e667f3bcc, 0x4006a09e667f3bcd, 0xb020000000000000,
0xaca765753908cd20, 0x3030000000000000, 0x2ca765753908cd20, 0xb030000000000000 },
{ 0x3006a09e667f3bcd, 0x4006a09e667f3bcd, 0xb020000000000000,
0x2cd3b3efbf5e2229, 0x3030000000000000, 0xacd3b3efbf5e2229, 0xb030000000000000 },
{ 0x3006a09e667f3bcc, 0x4006a09e667f3bcd, 0xb060003450000000,
0xb05e0068a0000000, 0x3061003450000000, 0x305e0068a0000000, 0xb061003450000000 },
};

int test23(long arg)
{
long i;
unsigned long results[4];
struct fmavals *vp = fmavals;

set_fpscr(FPS_RN_NEAR);
for (i = 0; i < sizeof(fmavals) / sizeof(fmavals[0]); ++i, ++vp) {
asm("lfd 6,0(%0); lfd 7,8(%0); lfd 8,16(%0); fmadd 0,6,7,8; stfd 0,0(%1)"
: : "b" (&vp->ra), "b" (results) : "memory");
asm("fmsub 1,6,7,8; fnmadd 2,6,7,8; fnmsub 3,6,7,8; stfd 1,8(%0); stfd 2,16(%0); stfd 3,24(%0)"
: : "b" (results) : "memory");
if (results[0] != vp->fma || results[1] != vp->fms ||
results[2] != vp->nfma || results[3] != vp->nfms) {
print_hex(i, 2, " ");
print_hex(results[0], 16, " ");
print_hex(results[1], 16, " ");
print_hex(results[2], 16, " ");
print_hex(results[3], 16, "\r\n");
return i + 1;
}
}
return 0;
}

int fpu_test_23(void)
{
enable_fp();
return trapit(0, test23);
}

int fail = 0;

void do_test(int num, int (*test)(void))
@ -1385,6 +1455,7 @@ int main(void)
do_test(20, fpu_test_20);
do_test(21, fpu_test_21);
do_test(22, fpu_test_22);
do_test(23, fpu_test_23);

return fail;
}

BIN
tests/test_fpu.bin
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1
tests/test_fpu.console_out
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@ -20,3 +20,4 @@ test 19:PASS
test 20:PASS
test 21:PASS
test 22:PASS
test 23:PASS

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