main.cpp

#include <stdio.h>
#include <float.h>

extern "C" bool CalcMinMax(const float* a, int n, float* min, float* max);

bool CalcMinMaxCpp(const float* a, int n, float* min, float* max)
{
    if (n <= 0)
        return false;

    float min_a = FLT_MAX;
    float max_a = -FLT_MAX;

    for (int i = 0; i < n; i++)
    {
        if (a[i] < min_a)
            min_a = a[i];

        if (a[i] > max_a)
            max_a = a[i];
    }

    *min = min_a;
    *max = max_a;
    return true;
}

int main(int argc, char* argv[])
{
    float a[] = { 20, -12, 42, 97, 14, -26, 57, 74, -18, 63, 34, -9};
    const int n = sizeof(a) / sizeof(float);
    float min1, max1;
    float min2, max2;

    CalcMinMaxCpp(a, n, &min1, &max1);
    CalcMinMax(a, n, &min2, &max2);

    for (int i = 0; i < n; i++)
        printf("a[%2d] = %8.2f\n", i, a[i]);

    printf("\n");
    printf("min1: %8.2f  max1: %8.2f\n", min1, max1);
    printf("min2: %8.2f  max2: %8.2f\n", min2, max2);
}

calcminmax.asm

; Name:     calcminmax.asm
;
; Build:    g++ -c -m32 main.cpp -o main.o
;           nasm -f elf32 -o calcminmax.o calcminmax.asm
;           g++ -m32 -o calcminmax calcminmax.o main.o
;
; Source:   Modern x86 Assembly Language Programming p.116

global  CalcMinMax

section .data

r4_MinFloat dq 0xff7fffff                ;smallest float number
r4_MaxFloat dq 0x7f7fffff                ;largest float number

section .text

; extern "C" bool CalcMinMax(const float* a, int n, float* min, float* max);
;
; Description:  The following function calculates the min and max values
;               of a single-precision floating-point array.
;
; Returns:      0 = invalid 'n'
;               1 = valid 'n'

%define a   [ebp+8]
%define n   [ebp+12]
%define min [ebp+16]
%define max [ebp+20]

CalcMinMax:
    push    ebp
    mov     ebp,esp
; Load argument values and make sure 'n' is valid.
    xor     eax,eax                     ;set error return code
    mov     edx,a                       ;edx = 'a'
    mov     ecx,n                       ;ecx = 'n'
    test    ecx,ecx
    jle     .done                       ;jump if 'n' <= 0
    fld     qword[r4_MinFloat]          ;initial max_a value
    fld     qword[r4_MaxFloat]          ;initial min_a value
; Find min and max of input array
.l1:
    fld     dword[edx]                  ;load *a
    fld     st0                         ;duplicate *a on stack
    fcomi   st0,st2                     ;compare *a with min
    fcmovnb st0,st2                     ;ST(0) equals smaller val
    fstp    st2                         ;save new min value
    fcomi   st0,st2                     ;compare *a with max_a
    fcmovb  st0,st2                     ;st(0) equals larger val
    fstp    st2                         ;save new max value
    add     edx,4                       ;point to next a[i]
    dec     ecx
    jnz     .l1                         ;repeat loop until finished
; Save results
    mov     eax,min
    fstp    dword[eax]                  ;save final min
    mov     eax,max    
    fstp    dword[eax]                  ;save final max
    mov     eax,1                       ;set success return code
.done:
    pop     ebp
    ret

build

g++ -c -m32 main.cpp -o main.o
nasm -f elf32 -o calcminmax.o calcminmax.asm
g++ -m32 -o calcminmax calcminmax.o main.o