70,021
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movq %rax, -24(%rbp) | movq %rax, -24(%rbp)
movsd -16(%rbp), %xmm0 | movsd -16(%rbp), %xmm0
movapd %xmm0, %xmm1 | movapd %xmm0, %xmm1
mulsd -24(%rbp), %xmm1 | mulsd -24(%rbp), %xmm1
movsd -8(%rbp), %xmm0 | movsd -8(%rbp), %xmm0
divsd %xmm1, %xmm0 | divsd %xmm1, %xmm0
--------------------------------------| cvttsd2si %xmm0, %eax
--------------------------------------| cvtsi2sd %eax, %xmm0
movsd %xmm0, -32(%rbp) | movsd %xmm0, -32(%rbp)
movl $0, %eax | movl $0, %eax
leave | leave
ret | ret
可以在执行时看看xmm0的值是多少,应该不是完全等于500.0
而精度就在cvttsd2si和cvtsi2sd的转来转去中丢失掉了。
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#define DBL_DIG 15 /* # of decimal digits of precision */
#define DBL_EPSILON 2.2204460492503131e-016 /* smallest such that 1.0+DBL_EPSILON != 1.0 */
#define DBL_MANT_DIG 53 /* # of bits in mantissa */
#define DBL_MAX 1.7976931348623158e+308 /* max value */
#define DBL_MAX_10_EXP 308 /* max decimal exponent */
#define DBL_MAX_EXP 1024 /* max binary exponent */
#define DBL_MIN 2.2250738585072014e-308 /* min positive value */
#define DBL_MIN_10_EXP (-307) /* min decimal exponent */
#define DBL_MIN_EXP (-1021) /* min binary exponent */
#define _DBL_RADIX 2 /* exponent radix */
#define _DBL_ROUNDS 1 /* addition rounding: near */
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