Sylpheed/tools/ppc-manual/memory/lfd.md

lfd — Load Floating-Point Double

Category: Memory · Form: D · Opcode: 0xc8000000

Assembler Mnemonics

Mnemonic	XML entry	Flags	Description
lfd	lfd	—	Load Floating-Point Double
lfdu	lfdu	—	Load Floating-Point Double with Update
lfdux	lfdux	—	Load Floating-Point Double with Update Indexed
lfdx	lfdx	—	Load Floating-Point Double Indexed

Syntax

lfd [FD], [d]([RA0])
lfdu [FD], [d]([RA])
lfdux [FD], [RA], [RB]
lfdx [FD], [RA0], [RB]

Encoding

lfd — form D

• Opcode word: 0xc8000000
• Primary opcode (bits 0–5): 50
• Extended opcode: —
• Synchronising: no

Bits	Field	Meaning
0–5	OPCD	primary opcode
6–10	RT	destination GPR (or RS when storing)
11–15	RA	source GPR (0 ⇒ literal 0 for RA0 forms)
16–31	D/SI/UI	16-bit signed or unsigned immediate

lfdu — form D

• Opcode word: 0xcc000000
• Primary opcode (bits 0–5): 51
• Extended opcode: —
• Synchronising: no

Bits	Field	Meaning
0–5	OPCD	primary opcode
6–10	RT	destination GPR (or RS when storing)
11–15	RA	source GPR (0 ⇒ literal 0 for RA0 forms)
16–31	D/SI/UI	16-bit signed or unsigned immediate

lfdux — form X

• Opcode word: 0x7c0004ee
• Primary opcode (bits 0–5): 31
• Extended opcode: 631
• Synchronising: no

Bits	Field	Meaning
0–5	OPCD	primary opcode
6–10	RT/FRT/VRT	destination
11–15	RA/FRA/VRA	source A
16–20	RB/FRB/VRB	source B
21–30	XO	extended opcode (10 bits)
31	Rc	record-form flag

lfdx — form X

• Opcode word: 0x7c0004ae
• Primary opcode (bits 0–5): 31
• Extended opcode: 599
• Synchronising: no

Bits	Field	Meaning
0–5	OPCD	primary opcode
6–10	RT/FRT/VRT	destination
11–15	RA/FRA/VRA	source A
16–20	RB/FRB/VRB	source B
21–30	XO	extended opcode (10 bits)
31	Rc	record-form flag

Operands

Field	Role	Description
RA0	lfd: read; lfdx: read	Source GPR; when the encoded register number is 0 the operand is the literal 64-bit zero, not r0.
d	lfd: read; lfdu: read	16-bit signed displacement (d) added to the base address register.
FD	lfd: write; lfdu: write; lfdux: write; lfdx: write	Destination floating-point register.
RA	lfdu: read; lfdu: write; lfdux: read; lfdux: write	Source GPR (r0–r31).
RB	lfdux: read; lfdx: read	Source GPR.

Register Effects

lfd

• Reads (always): RA0, d
• Reads (conditional): none
• Writes (always): FD
• Writes (conditional): none

lfdu

• Reads (always): RA, d
• Reads (conditional): none
• Writes (always): FD, RA
• Writes (conditional): none

lfdux

• Reads (always): RA, RB
• Reads (conditional): none
• Writes (always): FD, RA
• Writes (conditional): none

lfdx

• Reads (always): RA0, RB
• Reads (conditional): none
• Writes (always): FD
• Writes (conditional): none

Status-Register Effects

No condition-register or status-register effects.

Operation (pseudocode)

EA <- (RA|0) + EXTS(d)
FRT <- MEM(EA, 8)

C Translation Example

/* No hand-written C yet. Translate the Canary emitter snapshot   */
/* under Implementation References; its HIR maps directly:        */
/*   f.LoadGPR(n) / f.StoreGPR(n, v)  -> r[n] / r[n] = v          */
/*   f.LoadFPR / StoreFPR, f.LoadVR / StoreVR -> f[n], v[n]        */
/*   f.Load(ea, T), f.Store(ea, v) -> raw read / write; emitters   */
/*     wrap them in f.ByteSwap for the big-endian guest value      */
/*   f.UpdateCR(n, v)  -> CR field n from v's LOW 32 BITS vs 0     */
/*   f.LoadCA / f.StoreCA -> xer.CA;  f.StoreSAT -> vscr.SAT       */
/*   i.XO.RA, i.D.DS, ... -> the bit-fields listed under Operands  */
/* The Register Effects and Status-Register Effects tables above  */
/* enumerate every side effect a faithful translation must emit.  */

Implementation References

lfd

• Canary XML: tools/ppc-instructions.xml — search for mnem="lfd"
• Canary emitter: src/xenia/cpu/ppc/ppc_emit_memory.cc:912
• Sylpheed opcode: crates/sylpheed-ppc/src/opcode.rs:113
• Sylpheed decoder: crates/sylpheed-ppc/src/decoder.rs:488

Canary emitter (frozen snapshot @ f21ebd49e9)

int InstrEmit_lfd(PPCHIRBuilder& f, const InstrData& i) {
  // if RA = 0 then
  //   b <- 0
  // else
  //   b <- (RA)
  // EA <- b + EXTS(D)
  // FRT <- MEM(EA, 8)
  Value* ea = CalculateEA_0_i(f, i.D.RA, XEEXTS16(i.D.DS));
  Value* rt = f.Cast(f.ByteSwap(f.Load(ea, INT64_TYPE)), FLOAT64_TYPE);
  f.StoreFPR(i.D.RT, rt);
  return 0;
}

lfdu

• Canary XML: tools/ppc-instructions.xml — search for mnem="lfdu"
• Canary emitter: src/xenia/cpu/ppc/ppc_emit_memory.cc:925
• Sylpheed opcode: crates/sylpheed-ppc/src/opcode.rs:114
• Sylpheed decoder: crates/sylpheed-ppc/src/decoder.rs:489

Canary emitter (frozen snapshot @ f21ebd49e9)

int InstrEmit_lfdu(PPCHIRBuilder& f, const InstrData& i) {
  // EA <- (RA) + EXTS(D)
  // FRT <- MEM(EA, 8)
  // RA <- EA
  Value* ea = CalculateEA_i(f, i.D.RA, XEEXTS16(i.D.DS));
  Value* rt = f.Cast(f.ByteSwap(f.Load(ea, INT64_TYPE)), FLOAT64_TYPE);
  f.StoreFPR(i.D.RT, rt);
  StoreEA(f, i.D.RA, ea);
  return 0;
}

lfdux

• Canary XML: tools/ppc-instructions.xml — search for mnem="lfdux"
• Canary emitter: src/xenia/cpu/ppc/ppc_emit_memory.cc:936
• Sylpheed opcode: crates/sylpheed-ppc/src/opcode.rs:115
• Sylpheed decoder: crates/sylpheed-ppc/src/decoder.rs:942

Canary emitter (frozen snapshot @ f21ebd49e9)

int InstrEmit_lfdux(PPCHIRBuilder& f, const InstrData& i) {
  // EA <- (RA) + (RB)
  // FRT <- MEM(EA, 8)
  // RA <- EA
  Value* ea = CalculateEA(f, i.X.RA, i.X.RB);
  Value* rt = f.Cast(f.ByteSwap(f.Load(ea, INT64_TYPE)), FLOAT64_TYPE);
  f.StoreFPR(i.X.RT, rt);
  StoreEA(f, i.X.RA, ea);
  return 0;
}

lfdx

• Canary XML: tools/ppc-instructions.xml — search for mnem="lfdx"
• Canary emitter: src/xenia/cpu/ppc/ppc_emit_memory.cc:947
• Sylpheed opcode: crates/sylpheed-ppc/src/opcode.rs:116
• Sylpheed decoder: crates/sylpheed-ppc/src/decoder.rs:941

Canary emitter (frozen snapshot @ f21ebd49e9)

int InstrEmit_lfdx(PPCHIRBuilder& f, const InstrData& i) {
  // if RA = 0 then
  //   b <- 0
  // else
  //   b <- (RA)
  // EA <- b + (RB)
  // FRT <- MEM(EA, 8)
  Value* ea = CalculateEA_0(f, i.X.RA, i.X.RB);
  Value* rt = f.Cast(f.ByteSwap(f.Load(ea, INT64_TYPE)), FLOAT64_TYPE);
  f.StoreFPR(i.X.RT, rt);
  return 0;
}

Special Cases & Edge Conditions

• Bit-exact double load. Reads 8 bytes and places them directly into FRT as IEEE-754 binary64. No format conversion is performed (contrast lfs, which expands single→double).
• No FPSCR side effects. lfd cannot raise IEEE exceptions: it neither rounds nor inspects the value. A signalling NaN read this way stays a signalling NaN until it is consumed by an arithmetic op.
• RA0 semantics. In the non-update forms (lfd, lfdx), RA = 0 selects literal zero — lfd FT, 0(0) loads from absolute address 0. Update forms lfdu / lfdux invoke RA = 0 and RA = RT (here RA is GPR; RT is FPR, so the latter cannot collide) as invalid forms when RA = 0.
• Alignment. Xenon tolerates unaligned 8-byte FP loads; PowerISA technically permits implementations to raise alignment exceptions for FP loads, so portable code uses 8-byte aligned addresses.
• Big-endian read. Bytes are interpreted big-endian: byte at EA is bits 0–7 of the IEEE pattern (sign + part of exponent), byte at EA+7 is bits 56–63 of the mantissa. mem.read_f64 in xenia handles the host-side byte-swap.
• MSR[FP] required. Like all FP-register accesses, lfd requires the FP unit be enabled (MSR[FP]=1). Otherwise a Floating-Point Unavailable interrupt is raised. Xenia assumes FP is always enabled in user code.
• Pair with stfd. Store-double is the symmetric counterpart.

Related Instructions

• lfs — single-precision load with format conversion to double.
• stfd, stfdu, stfdx, stfdux — corresponding stores.
• stfiwx — store-FP-as-integer-word (the asymmetric oddity in the FP load/store family).
• ld — integer doubleword load (same width, GPR target).

IBM Reference

• AIX 7.3 — lfd (Load Floating-Point Double)
• AIX 7.3 — lfdu / lfdx / lfdux