For returning multiple doubles, “res” should be an f64vector, and the third parameter of ___F64VECTORSET is the double value (no conversion required).

Marc

On Dec 22, 2019, at 7:30 AM, Ryuho Yokoyama ryuho8@gmail.com wrote:

[gambit-list] FFI C out parameters https://mailman.iro.umontreal.ca/pipermail/gambit-list/2015-January/007696.h...

According to the mailing list entry above:

multiple "int" values:

(c-declare "

void add_mul(int x, int y, ___SCMOBJ res) {

int add = x+y; int mul = x*y;

___VECTORSET(res, ___FIX(0), ___FIX(add)) ___VECTORSET(res, ___FIX(1), ___FIX(mul)) } ")

(define (add-mul x y) (let ((res (vector 0 0))) ((c-lambda (int int scheme-object) void "add_mul") x y res) (values (vector-ref res 0) (vector-ref res 1))))

(receive (add mul) (add-mul 3 7) (pp (list 'add= add 'mul= mul)))

;; prints: (add= 10 mul= 21)

In an example code, C function is returning multiple "int" values. How to write an example code returning multiple "double" values from a C function ?

multiple "double" values:

(c-declare "

void add_mul(double x, double y, ___SCMOBJ res) {

double add = x+y; double mul = x*y;

___F64VECTORSET(res, ___FIX(0), ___???(add)) ___F64VECTORSET(res, ___FIX(1), ___???(mul)) } ")

(define (add-mul x y) (let ((res (vector 0 0))) ((c-lambda (double double scheme-object) void "add_mul") x y res) (values (vector-ref res 0) (vector-ref res 1))))

(receive (add mul) (add-mul 3.5 7.0) (pp (list 'add= add 'mul= mul)))

;; prints: (add= 10.5 mul= 24.5)

___F64VECTORSET(res, ___FIX(0), ___???(add)) ↑ ↑ ?? ??

1. Is it possible to use ___F64VECTORSET macro instead of ___VECTORSET macro ?

2. Is it possible to define a ___F64(x) macro like a macro ___FIX(x) ?

Thank you very much in advance.

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