#include
#include
union uint_float
{
unsigned int i;
float f;
};
float calculate_machine_epsilon(float start)
{
union uint_float v;
v.f = start;
v.i++;
return v.f - start;
}
int main()
{
printf("%f\n", calculate_machine_epsilon(1.0));
return 0;
}
#if 0
/*
* intel
*/
0000000000001149 :
1149: f3 0f 1e fa endbr64
114d: 55 push %rbp
114e: 48 89 e5 mov %rsp,%rbp
1151: f3 0f 11 45 ec movss %xmm0,-0x14(%rbp) // (rbp-0x14)=0x3f800000
1156: f3 0f 10 45 ec movss -0x14(%rbp),%xmm0 // xmm0=0x3f800000
115b: f3 0f 11 45 fc movss %xmm0,-0x4(%rbp) // (rbp-0x4)=0x3f800000
1160: 8b 45 fc mov -0x4(%rbp),%eax // eax=0x3f800000
1163: 83 c0 01 add $0x1,%eax // eax=0x3f800001
1166: 89 45 fc mov %eax,-0x4(%rbp) // (rbp-0x4)=0x3f800001
1169: f3 0f 10 45 fc movss -0x4(%rbp),%xmm0 // xmm0=0x3f800001
116e: f3 0f 5c 45 ec subss -0x14(%rbp),%xmm0 // 0x3f800001-0x3f800000=0x34000000 -->
// 1.0000001192092896 - 1.0 = 1.1920928955078125e-7
1173: 5d pop %rbp
1174: c3 retq
0000000000001175 :
1175: f3 0f 1e fa endbr64
1179: 55 push %rbp
117a: 48 89 e5 mov %rsp,%rbp
117d: f3 0f 10 05 83 0e 00 movss 0xe83(%rip),%xmm0 # 2008 <_IO_stdin_used+0x8> // xmm0=0x3f800000=1.0
1184: 00
1185: e8 bf ff ff ff callq 1149
118a: f3 0f 5a c0 cvtss2sd %xmm0,%xmm0 // xmm0=0x3e80000000000000
118e: 48 8d 3d 6f 0e 00 00 lea 0xe6f(%rip),%rdi # 2004 <_IO_stdin_used+0x4>
1195: b8 01 00 00 00 mov $0x1,%eax
119a: e8 b1 fe ff ff callq 1050 // 0.000000
119f: b8 00 00 00 00 mov $0x0,%eax
11a4: 5d pop %rbp
11a5: c3 retq
11a6: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
11ad: 00 00 00
/*
* arm
*/
000000000040055c :
40055c: d10083ff sub sp, sp, #0x20
400560: bd000fe0 str s0, [sp, #12]
400564: bd400fe0 ldr s0, [sp, #12]
400568: bd001be0 str s0, [sp, #24]
40056c: b9401be0 ldr w0, [sp, #24]
400570: 11000400 add w0, w0, #0x1
400574: b9001be0 str w0, [sp, #24]
400578: bd401be1 ldr s1, [sp, #24]
40057c: bd400fe0 ldr s0, [sp, #12]
400580: 1e203820 fsub s0, s1, s0
400584: 910083ff add sp, sp, #0x20
400588: d65f03c0 ret
000000000040058c :
40058c: a9bf7bfd stp x29, x30, [sp, #-16]!
400590: 910003fd mov x29, sp
400594: 1e2e1000 fmov s0, #1.000000000000000000e+00
400598: 97fffff1 bl 40055c
40059c: 1e22c000 fcvt d0, s0
4005a0: 90000000 adrp x0, 400000 <_init-0x3e8>
4005a4: 9119a000 add x0, x0, #0x668
4005a8: 97ffffaa bl 400450
4005ac: 52800000 mov w0, #0x0 // #0
4005b0: a8c17bfd ldp x29, x30, [sp], #16
4005b4: d65f03c0 ret
#endif
