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Add support for comparisons against integer immediates

* libguile/vm-engine.c (s64-imm=?, u64-imm<?, imm-u64<?, s64-imm<?)
  (imm-s64<?): New instructions.
* libguile/instructions.c (FOR_EACH_INSTRUCTION_WORD_TYPE): Add new
  X8_S12_Z12 word type used by the new S64/immediate instructions.  A
  Z12 is a 12-bit signed integer immediate.
* module/system/vm/assembler.scm: Export new instructions, and add
  X8_S12_Z12 support.  Also, add missing shufflers for X8_S12_C12.
* module/language/bytecode.scm (compute-instruction-arity):
* module/system/vm/disassembler.scm (unpack-s12, disassembler): Add
  support for X8_S12_Z12.
* module/language/cps/types.scm (define-predicate-inferrer/param): New
  helper.
  (u64-=, u64-<, s64-<): Remove type checkers; this procedure does not
  cause &type-check.
  (u64-imm=?, s64-imm=?, u64-imm<?, imm-u64<?, s64-imm<?, imm-s64<?):
  New type inferrers.
* module/language/cps/type-fold.scm (define-unary-branch-folder*): New
  helper.
  (u64-imm=?, s64-imm=?, u64-imm<?, imm-u64<?, s64-imm<?, imm-s64<?):
  New branch folders.
* module/language/cps/reify-primitives.scm (reify-primitives): Reify
  constants for new immediate branching primcalls if values out of
  range.
* module/language/cps/effects-analysis.scm: Add support for new
  primcalls.
* module/language/cps/compile-bytecode.scm (compile-function): Add
  support for new primcalls and instructions.  Compile u64-imm-= to
  s64-imm=?.
This commit is contained in:
Andy Wingo 2017-11-14 10:41:24 +01:00
parent 4a0a930f1c
commit 294dbaad35
12 changed files with 225 additions and 19 deletions

View file

@ -40,6 +40,7 @@ SCM_SYMBOL (sym_bang, "!");
M(X8_S8_I16) \ M(X8_S8_I16) \
M(X8_S12_S12) \ M(X8_S12_S12) \
M(X8_S12_C12) \ M(X8_S12_C12) \
M(X8_S12_Z12) \
M(X8_C12_C12) \ M(X8_C12_C12) \
M(X8_F12_F12) \ M(X8_F12_F12) \
M(X8_S8_S8_S8) \ M(X8_S8_S8_S8) \

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@ -4100,11 +4100,77 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
NEXT (1); NEXT (1);
} }
VM_DEFINE_OP (218, unused_218, NULL, NOP) VM_DEFINE_OP (218, s64_imm_numerically_equal, "s64-imm=?", OP1 (X8_S12_Z12))
VM_DEFINE_OP (219, unused_219, NULL, NOP) {
VM_DEFINE_OP (220, unused_220, NULL, NOP) scm_t_uint16 a;
VM_DEFINE_OP (221, unused_221, NULL, NOP) scm_t_int64 x, y;
VM_DEFINE_OP (222, unused_222, NULL, NOP)
a = (op >> 8) & 0xfff;
x = SP_REF_S64 (a);
y = ((scm_t_int32) op) >> 20; /* Sign extension. */
vp->compare_result = x == y ? SCM_F_COMPARE_EQUAL : SCM_F_COMPARE_NONE;
NEXT (1);
}
VM_DEFINE_OP (219, u64_imm_less, "u64-imm<?", OP1 (X8_S12_C12))
{
scm_t_uint16 a;
scm_t_uint64 x, y;
UNPACK_12_12 (op, a, y);
x = SP_REF_U64 (a);
vp->compare_result = x < y ? SCM_F_COMPARE_LESS_THAN : SCM_F_COMPARE_NONE;
NEXT (1);
}
VM_DEFINE_OP (220, imm_u64_less, "imm-u64<?", OP1 (X8_S12_C12))
{
scm_t_uint16 a;
scm_t_uint64 x, y;
UNPACK_12_12 (op, a, x);
y = SP_REF_U64 (a);
vp->compare_result = x < y ? SCM_F_COMPARE_LESS_THAN : SCM_F_COMPARE_NONE;
NEXT (1);
}
VM_DEFINE_OP (221, s64_imm_less, "s64-imm<?", OP1 (X8_S12_Z12))
{
scm_t_uint16 a;
scm_t_int64 x, y;
a = (op >> 8) & 0xfff;
x = SP_REF_S64 (a);
y = ((scm_t_int32) op) >> 20; /* Sign extension. */
vp->compare_result = x < y ? SCM_F_COMPARE_LESS_THAN : SCM_F_COMPARE_NONE;
NEXT (1);
}
VM_DEFINE_OP (222, imm_s64_less, "imm-s64<?", OP1 (X8_S12_Z12))
{
scm_t_uint16 a;
scm_t_int64 x, y;
a = (op >> 8) & 0xfff;
y = SP_REF_S64 (a);
x = ((scm_t_int32) op) >> 20; /* Sign extension. */
vp->compare_result = x < y ? SCM_F_COMPARE_LESS_THAN : SCM_F_COMPARE_NONE;
NEXT (1);
}
VM_DEFINE_OP (223, unused_223, NULL, NOP) VM_DEFINE_OP (223, unused_223, NULL, NOP)
VM_DEFINE_OP (224, unused_224, NULL, NOP) VM_DEFINE_OP (224, unused_224, NULL, NOP)
VM_DEFINE_OP (225, unused_225, NULL, NOP) VM_DEFINE_OP (225, unused_225, NULL, NOP)

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@ -42,6 +42,7 @@
((X8_S8_I16) 2) ((X8_S8_I16) 2)
((X8_S12_S12) 2) ((X8_S12_S12) 2)
((X8_S12_C12) 2) ((X8_S12_C12) 2)
((X8_S12_Z12) 2)
((X8_C12_C12) 2) ((X8_C12_C12) 2)
((X8_F12_F12) 2) ((X8_F12_F12) 2)
((X8_S8_S8_S8) 3) ((X8_S8_S8_S8) 3)

View file

@ -425,6 +425,12 @@
(binary op emit-je emit-jne a b)) (binary op emit-je emit-jne a b))
(define (binary-< emit-<? a b) (define (binary-< emit-<? a b)
(binary emit-<? emit-jl emit-jnl a b)) (binary emit-<? emit-jl emit-jnl a b))
(define (binary-test/imm op a b)
(op asm (from-sp (slot a)) b)
(emit-branch emit-je emit-jne))
(define (binary-</imm op a b)
(op asm (from-sp (slot a)) b)
(emit-branch emit-jl emit-jnl))
(match exp (match exp
(($ $primcall 'heap-object? #f (a)) (unary emit-heap-object? a)) (($ $primcall 'heap-object? #f (a)) (unary emit-heap-object? a))
(($ $primcall 'null? #f (a)) (unary emit-null? a)) (($ $primcall 'null? #f (a)) (unary emit-null? a))
@ -451,9 +457,15 @@
(($ $primcall '< #f (a b)) (binary-< emit-<? a b)) (($ $primcall '< #f (a b)) (binary-< emit-<? a b))
(($ $primcall '= #f (a b)) (binary-test emit-=? a b)) (($ $primcall '= #f (a b)) (binary-test emit-=? a b))
(($ $primcall 'u64-< #f (a b)) (binary-< emit-u64<? a b)) (($ $primcall 'u64-< #f (a b)) (binary-< emit-u64<? a b))
(($ $primcall 'u64-imm-< b (a)) (binary-</imm emit-u64-imm<? a b))
(($ $primcall 'imm-u64-< b (a)) (binary-</imm emit-imm-u64<? a b))
(($ $primcall 'u64-= #f (a b)) (binary-test emit-u64=? a b)) (($ $primcall 'u64-= #f (a b)) (binary-test emit-u64=? a b))
(($ $primcall 'u64-imm-= b (a)) (binary-test/imm emit-s64-imm=? a b))
(($ $primcall 's64-= #f (a b)) (binary-test emit-u64=? a b))
(($ $primcall 's64-imm-= b (a)) (binary-test/imm emit-s64-imm=? a b))
(($ $primcall 's64-< #f (a b)) (binary-< emit-s64<? a b)) (($ $primcall 's64-< #f (a b)) (binary-< emit-s64<? a b))
(($ $primcall 's64-= #f (a b)) (binary-test emit-s64=? a b)) (($ $primcall 's64-imm-< b (a)) (binary-</imm emit-s64-imm<? a b))
(($ $primcall 'imm-s64-< b (a)) (binary-</imm emit-imm-s64<? a b))
(($ $primcall 'f64-< #f (a b)) (binary-< emit-f64<? a b)) (($ $primcall 'f64-< #f (a b)) (binary-< emit-f64<? a b))
(($ $primcall 'f64-= #f (a b)) (binary-test emit-f64=? a b)))) (($ $primcall 'f64-= #f (a b)) (binary-test emit-f64=? a b))))

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@ -424,9 +424,15 @@ is or might be a read or a write to the same location as A."
((= . _) &type-check) ((= . _) &type-check)
((< . _) &type-check) ((< . _) &type-check)
((u64-= . _)) ((u64-= . _))
((u64-imm-= . _))
((u64-< . _)) ((u64-< . _))
((u64-imm-< . _))
((imm-u64-< . _))
((s64-= . _)) ((s64-= . _))
((s64-imm-= . _))
((s64-< . _)) ((s64-< . _))
((s64-imm-< . _))
((imm-s64-< . _))
((f64-= . _)) ((f64-= . _))
((f64-< . _)) ((f64-< . _))
((zero? . _) &type-check) ((zero? . _) &type-check)

View file

@ -139,7 +139,6 @@ before it is lowered to CPS?"
u64-= u64-=
s64-< s64-<
s64-=
f64-< f64-<
f64-=)) f64-=))

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@ -153,12 +153,13 @@
($continue kb src ($const b)))))) ($continue kb src ($const b))))))
(($ $kargs names vars ($ $continue k src ($ $primcall name param args))) (($ $kargs names vars ($ $continue k src ($ $primcall name param args)))
(cond (cond
((or (prim-instruction name) (branching-primitive? name)) ((prim-instruction name)
;; Assume arities are correct. ;; Assume arities are correct.
(let () (let ()
(define (u6? val) (and (exact-integer? val) (<= 0 val 63))) (define (u6? val) (and (exact-integer? val) (<= 0 val 63)))
(define (u8? val) (and (exact-integer? val) (<= 0 val 255))) (define (u8? val) (and (exact-integer? val) (<= 0 val 255)))
(define-syntax-rule (reify-constants wrap (define-syntax-rule (reify-constants
wrap
((op (pred? c) in ...) (op* out ...)) ((op (pred? c) in ...) (op* out ...))
... ...
(_ default)) (_ default))
@ -211,6 +212,42 @@
($continue k src ($call proc args)))) ($continue k src ($call proc args))))
(let$ body (resolve-prim name kproc src)) (let$ body (resolve-prim name kproc src))
(setk label ($kargs names vars ,body)))))) (setk label ($kargs names vars ,body))))))
(($ $kargs names vars
($ $continue kf src ($ $branch kt ($ $primcall name param args))))
(let ()
(define (u11? val) (<= 0 val #x7ff))
(define (u12? val) (<= 0 val #xfff))
(define (s12? val) (<= (- #x800) val #x7ff))
(define-syntax-rule (reify-constants ((op (pred? c) in ...)
wrap-op (op* out ...))
...
(_ default))
(match name
('op
(if (pred? param)
cps
(match args
((in ...)
(with-cps cps
(letv c)
(letk kconst
($kargs ('c) (c)
($continue kf src
($branch kt ($primcall 'op* #f (out ...))))))
(setk label
($kargs names vars
($continue kconst src
($primcall 'wrap-op param ())))))))))
...
(_ default)))
(reify-constants
((u64-imm-= (u11? b) a) load-u64 (u64-= a b))
((u64-imm-< (u12? b) a) load-u64 (u64-< a b))
((imm-u64-< (u12? a) b) load-u64 (u64-< a b))
((s64-imm-= (s12? b) a) load-s64 (s64-= a b))
((s64-imm-< (s12? b) a) load-s64 (s64-< a b))
((imm-s64-< (s12? a) b) load-s64 (s64-< a b))
(_ cps))))
(($ $kargs names vars ($ $continue k src ($ $call proc args))) (($ $kargs names vars ($ $continue k src ($ $call proc args)))
(with-cps cps (with-cps cps
(let$ k (uniquify-receive k)) (let$ k (uniquify-receive k))

View file

@ -203,7 +203,7 @@
($primcall unbox-a #f (scm)))))) ($primcall unbox-a #f (scm))))))
(define (specialize-fixnum-comparison cps kf kt src op a b) (define (specialize-fixnum-comparison cps kf kt src op a b)
(let ((op (symbol-append 's64- op))) (let ((op (match op ('= 'u64-=) ('< 's64-<))))
(with-cps cps (with-cps cps
(letv s64-a s64-b) (letv s64-a s64-b)
(letk kop ($kargs ('s64-b) (s64-b) (letk kop ($kargs ('s64-b) (s64-b)
@ -217,7 +217,7 @@
($primcall 'untag-fixnum #f (a))))))) ($primcall 'untag-fixnum #f (a)))))))
(define (specialize-fixnum-scm-comparison cps kf kt src op a-fx b-scm) (define (specialize-fixnum-scm-comparison cps kf kt src op a-fx b-scm)
(let ((s64-op (match op ('= 's64-=) ('< 's64-<)))) (let ((s64-op (match op ('= 'u64-=) ('< 's64-<))))
(with-cps cps (with-cps cps
(letv a b sunk) (letv a b sunk)
(letk kheap ($kargs ('sunk) (sunk) (letk kheap ($kargs ('sunk) (sunk)

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@ -51,9 +51,13 @@
(define-syntax-rule (define-branch-folder-alias to from) (define-syntax-rule (define-branch-folder-alias to from)
(hashq-set! *branch-folders* 'to (hashq-ref *branch-folders* 'from))) (hashq-set! *branch-folders* 'to (hashq-ref *branch-folders* 'from)))
(define-syntax-rule (define-unary-branch-folder (name arg min max) body ...) (define-syntax-rule (define-unary-branch-folder* (name param arg min max)
body ...)
(define-branch-folder name (lambda (param arg min max) body ...))) (define-branch-folder name (lambda (param arg min max) body ...)))
(define-syntax-rule (define-unary-branch-folder (name arg min max) body ...)
(define-unary-branch-folder* (name param arg min max) body ...))
(define-syntax-rule (define-binary-branch-folder (name arg0 min0 max0 (define-syntax-rule (define-binary-branch-folder (name arg0 min0 max0
arg1 min1 max1) arg1 min1 max1)
body ...) body ...)
@ -151,13 +155,33 @@
;; ;;
;; (define-branch-folder-alias f64-< <) ;; (define-branch-folder-alias f64-< <)
(define-unary-branch-folder* (u64-imm-= c type min max)
(cond
((= c min max) (values #t #t))
((<= min c max) (values #f #f))
(else (values #t #f))))
(define-branch-folder-alias s64-imm-= u64-imm-=)
(define-unary-branch-folder* (u64-imm-< c type min max)
(cond
((< max c) (values #t #t))
((>= min c) (values #t #f))
(else (values #f #f))))
(define-branch-folder-alias s64-imm-< u64-imm-<)
(define-unary-branch-folder* (imm-u64-< c type min max)
(cond
((< c min) (values #t #t))
((>= c max) (values #t #f))
(else (values #f #f))))
(define-branch-folder-alias imm-s64-< imm-u64-<)
(define-binary-branch-folder (= type0 min0 max0 type1 min1 max1) (define-binary-branch-folder (= type0 min0 max0 type1 min1 max1)
(case (compare-integer-ranges type0 min0 max0 type1 min1 max1) (case (compare-integer-ranges type0 min0 max0 type1 min1 max1)
((=) (values #t #t)) ((=) (values #t #t))
((< >) (values #t #f)) ((< >) (values #t #f))
(else (values #f #f)))) (else (values #f #f))))
(define-branch-folder-alias u64-= =) (define-branch-folder-alias u64-= =)
(define-branch-folder-alias s64-= =)

View file

@ -471,6 +471,12 @@ minimum, and maximum."
(let ((true? (not (zero? succ)))) (let ((true? (not (zero? succ))))
body ...))) body ...)))
(define-syntax-rule (define-predicate-inferrer/param
(name param arg ... true?) body ...)
(define-type-inferrer* (name param succ arg ...)
(let ((true? (not (zero? succ))))
body ...)))
(define-syntax define-simple-type-checker (define-syntax define-simple-type-checker
(lambda (x) (lambda (x)
(define (parse-spec l) (define (parse-spec l)
@ -1007,16 +1013,31 @@ minimum, and maximum."
(define-simple-type-checker (< &real &real)) (define-simple-type-checker (< &real &real))
(define-<-inferrer (< &real &exact-integer)) (define-<-inferrer (< &real &exact-integer))
(define-simple-type-checker (u64-= &u64 &u64))
(define-=-inferrer (u64-= &u64)) (define-=-inferrer (u64-= &u64))
(define-simple-type-checker (u64-< &u64 &u64))
(define-<-inferrer (u64-< &u64 &u64)) (define-<-inferrer (u64-< &u64 &u64))
(define-simple-type-checker (s64-= &s64 &s64))
(define-=-inferrer (s64-= &s64))
(define-simple-type-checker (s64-< &s64 &s64))
(define-<-inferrer (s64-< &s64 &s64)) (define-<-inferrer (s64-< &s64 &s64))
(define-predicate-inferrer/param (u64-imm-= b a true?)
(when true?
(restrict! a (logior &u64 &s64) (max (&min a) b) (min (&max a) b))))
(define-predicate-inferrer/param (u64-imm-< b a true?)
(if true?
(restrict! a (logior &u64 &s64) (&min a) (min (&max a) (1- b)))
(restrict! a (logior &u64 &s64) (max (&min a) b) (&max a))))
(define-predicate-inferrer/param (imm-u64-< b a true?)
(if true?
(restrict! a (logior &u64 &s64) (max (1+ (&min a)) b) (&max a))
(restrict! a (logior &u64 &s64) (&min a) (min (&max a) b))))
(define-type-aliases u64-imm-= s64-imm-=)
(define-type-aliases u64-imm-< s64-imm-<)
(define-type-aliases imm-u64-< imm-s64-<)
;; Unfortunately, we can't define f64 comparison inferrers because of ;; Unfortunately, we can't define f64 comparison inferrers because of
;; not-a-number values. ;; not-a-number values.

View file

@ -66,8 +66,12 @@
emit-u64=? emit-u64=?
emit-u64<? emit-u64<?
emit-s64=? emit-u64-imm<?
emit-imm-u64<?
emit-s64-imm=?
emit-s64<? emit-s64<?
emit-s64-imm<?
emit-imm-s64<?
emit-f64=? emit-f64=?
emit-f64<? emit-f64<?
emit-=? emit-=?
@ -341,6 +345,12 @@
(z (check-urange z #xfff))) (z (check-urange z #xfff)))
(logior x (ash y 8) (ash z 20)))) (logior x (ash y 8) (ash z 20))))
(define-inline (pack-u8-u12-s12 x y z)
(let ((x (check-urange x #xff))
(y (check-urange y #xfff))
(z (check-srange z #xfff)))
(logior x (ash y 8) (ash z 20))))
(define-inline (pack-u8-u8-u16 x y z) (define-inline (pack-u8-u8-u16 x y z)
(let ((x (check-urange x #xff)) (let ((x (check-urange x #xff))
(y (check-urange y #xff)) (y (check-urange y #xff))
@ -617,6 +627,8 @@ later by the linker."
(emit asm (pack-u8-u12-u12 opcode a b))) (emit asm (pack-u8-u12-u12 opcode a b)))
((X8_S12_C12 a b) ((X8_S12_C12 a b)
(emit asm (pack-u8-u12-u12 opcode a b))) (emit asm (pack-u8-u12-u12 opcode a b)))
((X8_S12_Z12 a b)
(emit asm (pack-u8-u12-s12 opcode a b)))
((X8_C12_C12 a b) ((X8_C12_C12 a b)
(emit asm (pack-u8-u12-u12 opcode a b))) (emit asm (pack-u8-u12-u12 opcode a b)))
((X8_F12_F12 a b) ((X8_F12_F12 a b)
@ -803,6 +815,14 @@ later by the linker."
(emit-push asm a) (emit-push asm a)
(encode-X8_S12_S12-X8_C24 asm 0 0 const opcode) (encode-X8_S12_S12-X8_C24 asm 0 0 const opcode)
(emit-pop asm dst)))) (emit-pop asm dst))))
(define (encode-X8_S12_C12!/shuffle asm a const opcode)
(cond
((< a (ash 1 12))
(encode-X8_S12_C12 asm a const opcode))
(else
(emit-push asm a)
(encode-X8_S12_C12 asm 0 const opcode)
(emit-drop asm 1))))
(define (encode-X8_S12_C12<-/shuffle asm dst const opcode) (define (encode-X8_S12_C12<-/shuffle asm dst const opcode)
(cond (cond
((< dst (ash 1 12)) ((< dst (ash 1 12))
@ -812,6 +832,14 @@ later by the linker."
(emit-push asm dst) (emit-push asm dst)
(encode-X8_S12_C12 asm 0 const opcode) (encode-X8_S12_C12 asm 0 const opcode)
(emit-pop asm dst)))) (emit-pop asm dst))))
(define (encode-X8_S12_Z12!/shuffle asm a const opcode)
(cond
((< a (ash 1 12))
(encode-X8_S12_Z12 asm a const opcode))
(else
(emit-push asm a)
(encode-X8_S12_Z12 asm 0 const opcode)
(emit-drop asm 1))))
(define (encode-X8_S8_I16<-/shuffle asm dst imm opcode) (define (encode-X8_S8_I16<-/shuffle asm dst imm opcode)
(cond (cond
((< dst (ash 1 8)) ((< dst (ash 1 8))
@ -877,7 +905,9 @@ later by the linker."
(('<- 'X8_S12_S12) #'encode-X8_S12_S12<-/shuffle) (('<- 'X8_S12_S12) #'encode-X8_S12_S12<-/shuffle)
(('! 'X8_S12_S12 'X8_C24) #'encode-X8_S12_S12-X8_C24!/shuffle) (('! 'X8_S12_S12 'X8_C24) #'encode-X8_S12_S12-X8_C24!/shuffle)
(('<- 'X8_S12_S12 'X8_C24) #'encode-X8_S12_S12-X8_C24<-/shuffle) (('<- 'X8_S12_S12 'X8_C24) #'encode-X8_S12_S12-X8_C24<-/shuffle)
(('! 'X8_S12_C12) #'encode-X8_S12_C12!/shuffle)
(('<- 'X8_S12_C12) #'encode-X8_S12_C12<-/shuffle) (('<- 'X8_S12_C12) #'encode-X8_S12_C12<-/shuffle)
(('! 'X8_S12_Z12) #'encode-X8_S12_Z12!/shuffle)
(('<- 'X8_S8_I16) #'encode-X8_S8_I16<-/shuffle) (('<- 'X8_S8_I16) #'encode-X8_S8_I16<-/shuffle)
(('! 'X8_S8_S8_S8) #'encode-X8_S8_S8_S8!/shuffle) (('! 'X8_S8_S8_S8) #'encode-X8_S8_S8_S8!/shuffle)
(('<- 'X8_S8_S8_S8) #'encode-X8_S8_S8_S8<-/shuffle) (('<- 'X8_S8_S8_S8) #'encode-X8_S8_S8_S8<-/shuffle)
@ -919,6 +949,7 @@ later by the linker."
('X8_S8_I16 #'(a imm)) ('X8_S8_I16 #'(a imm))
('X8_S12_S12 #'(a b)) ('X8_S12_S12 #'(a b))
('X8_S12_C12 #'(a b)) ('X8_S12_C12 #'(a b))
('X8_S12_Z12 #'(a b))
('X8_C12_C12 #'(a b)) ('X8_C12_C12 #'(a b))
('X8_F12_F12 #'(a b)) ('X8_F12_F12 #'(a b))
('X8_S8_S8_S8 #'(a b c)) ('X8_S8_S8_S8 #'(a b c))

View file

@ -72,6 +72,11 @@
s s
(- s (ash 1 24)))) (- s (ash 1 24))))
(define (unpack-s12 s)
(if (zero? (logand s (ash 1 11)))
s
(- s (ash 1 12))))
(define (unpack-s32 s) (define (unpack-s32 s)
(if (zero? (logand s (ash 1 31))) (if (zero? (logand s (ash 1 31)))
s s
@ -97,6 +102,9 @@
X8_F12_F12) X8_F12_F12)
#'((logand (ash word -8) #xfff) #'((logand (ash word -8) #xfff)
(ash word -20))) (ash word -20)))
((X8_S12_Z12)
#'((logand (ash word -8) #xfff)
(unpack-s12 (ash word -20))))
((X8_S8_S8_S8 ((X8_S8_S8_S8
X8_S8_S8_C8 X8_S8_S8_C8
X8_S8_C8_S8) X8_S8_C8_S8)