Sylpheed/tools/ppc-manual/vmx/vpkuhum.md

vpkuhum — Vector Pack Unsigned Half Word Unsigned Modulo

Category: VMX (Altivec) · Form: VX · Opcode: 0x1000000e

Assembler Mnemonics

Mnemonic	XML entry	Flags	Description
vpkuhum	vpkuhum	—	Vector Pack Unsigned Half Word Unsigned Modulo
vpkuhum128	vpkuhum128	—	Vector128 Pack Unsigned Half Word Unsigned Modulo

Syntax

vpkuhum [VD], [VA], [VB]
vpkuhum128 [VD], [VA], [VB]

Encoding

vpkuhum — form VX

• Opcode word: 0x1000000e
• Primary opcode (bits 0–5): 4
• Extended opcode: 14
• Synchronising: no

Bits	Field	Meaning
0–5	OPCD	primary opcode (4)
6–10	VRT/VD	destination vector register
11–15	VRA/VA	source A vector register
16–20	VRB/VB	source B vector register
21–31	XO	extended opcode (11 bits)

vpkuhum128 — form VX128

• Opcode word: 0x14000300
• Primary opcode (bits 0–5): 5
• Extended opcode: 768
• Synchronising: no

Bits	Field	Meaning
0–5	OPCD	primary opcode (4 or 5)
6–10	VD128l	destination low 5 bits
11–15	VA128l	source A low 5 bits
16–20	VB128l	source B low 5 bits
21	VA128H	source A high bit
22	—	reserved
23–25	VC	optional VC / XO sub-field
26	VA128h	source A middle bit
27	—	reserved
28–29	VD128h	destination high 2 bits
30–31	VB128h	source B high 2 bits

Operands

Field	Role	Description
VA	vpkuhum: read; vpkuhum128: read	Source A vector register.
VB	vpkuhum: read; vpkuhum128: read	Source B vector register.
VD	vpkuhum: write; vpkuhum128: write	Destination vector register.

Register Effects

vpkuhum

• Reads (always): VA, VB
• Reads (conditional): none
• Writes (always): VD
• Writes (conditional): none

vpkuhum128

• Reads (always): VA, VB
• Reads (conditional): none
• Writes (always): VD
• Writes (conditional): none

Status-Register Effects

No condition-register or status-register effects.

Operation (pseudocode)

; No hand-written pseudocode for this instruction yet.
; The authoritative semantics are the Canary emitter snapshot under
; Implementation References; about half of Canary's emitters open
; with the PPC-style definition as a comment (`RD <- (RA) + (RB)`).
; Every side effect is also enumerated in the Register Effects and
; Status-Register Effects tables above.

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

vpkuhum

• Canary XML: tools/ppc-instructions.xml — search for mnem="vpkuhum"
• Canary emitter: src/xenia/cpu/ppc/ppc_emit_altivec.cc:1895
• Sylpheed opcode: crates/sylpheed-ppc/src/opcode.rs:413
• Sylpheed decoder: crates/sylpheed-ppc/src/decoder.rs:555

Canary emitter (frozen snapshot @ f21ebd49e9)

int InstrEmit_vpkuhum(PPCHIRBuilder& f, const InstrData& i) {
  return InstrEmit_vpkuhum_(f, i.VX.VD, i.VX.VA, i.VX.VB);
}

// ── delegates to (src/xenia/cpu/ppc/ppc_emit_altivec.cc:1882) ──
int InstrEmit_vpkuhum_(PPCHIRBuilder& f, uint32_t vd, uint32_t va,
                       uint32_t vb) {
  // Vector Pack Unsigned Halfword Unsigned Modulo
  // Convert VA and VB from unsigned shorts to unsigned bytes then concat:
  // for each i in VA + VB:
  //   i = uint8_t(uint16_t(i))
  // dest = VA | VB (lower 8bit values)
  Value* v = f.Pack(f.LoadVR(va), f.LoadVR(vb),
                    PACK_TYPE_8_IN_16 | PACK_TYPE_IN_UNSIGNED |
                        PACK_TYPE_OUT_UNSIGNED | PACK_TYPE_OUT_UNSATURATE);
  f.StoreVR(vd, v);
  return 0;
}

vpkuhum128

• Canary XML: tools/ppc-instructions.xml — search for mnem="vpkuhum128"
• Canary emitter: src/xenia/cpu/ppc/ppc_emit_altivec.cc:1898
• Sylpheed opcode: crates/sylpheed-ppc/src/opcode.rs:414
• Sylpheed decoder: crates/sylpheed-ppc/src/decoder.rs:741

Canary emitter (frozen snapshot @ f21ebd49e9)

int InstrEmit_vpkuhum128(PPCHIRBuilder& f, const InstrData& i) {
  return InstrEmit_vpkuhum_(f, VX128_VD128, VX128_VA128, VX128_VB128);
}

// ── delegates to (src/xenia/cpu/ppc/ppc_emit_altivec.cc:1882) ──
int InstrEmit_vpkuhum_(PPCHIRBuilder& f, uint32_t vd, uint32_t va,
                       uint32_t vb) {
  // Vector Pack Unsigned Halfword Unsigned Modulo
  // Convert VA and VB from unsigned shorts to unsigned bytes then concat:
  // for each i in VA + VB:
  //   i = uint8_t(uint16_t(i))
  // dest = VA | VB (lower 8bit values)
  Value* v = f.Pack(f.LoadVR(va), f.LoadVR(vb),
                    PACK_TYPE_8_IN_16 | PACK_TYPE_IN_UNSIGNED |
                        PACK_TYPE_OUT_UNSIGNED | PACK_TYPE_OUT_UNSATURATE);
  f.StoreVR(vd, v);
  return 0;
}

Special Cases & Edge Conditions

• Unsigned half-word → byte modulo pack. Each of the 16 input half-word lanes (8 from VA, 8 from VB) is truncated to its low 8 bits. No saturation; values above 255 wrap modulo 256.
• VSCR[SAT] is never touched. This is the -m (modulo) form. For saturation use vpkuhus.
• Lane-count doubling. 16 half-word lanes → 16 byte lanes, VA's 8 half-words into VD.b[0..7] and VB's 8 into VD.b[8..15].
• Cheap "low-byte extract" primitive. Often used to repack per-channel results after a half-word arithmetic step. Contrast with shifting + masking.
• No Rc, no XER.
• VMX128 sibling vpkuhum128.

Related Instructions

• vpkuhus — the saturating sibling.
• vpkuwum — word → half-word modulo pack.
• vpkshss, vpkshus — signed half-word packs.
• vupkhub / vupklub (if present) — zero-extending byte → half-word unpacks that reverse this op.
• vperm — general-purpose alternative when the packing pattern is irregular.

IBM Reference

• AIX 7.3 — vpkuhum (Vector Pack Unsigned Half Word Unsigned Modulo)
• IBM AltiVec Technology Programmer's Interface Manual, Chapter 6 — Permute and Formatting