---
title: log10
description: "计算以10为底的对数值。"
url: https://www.hikunpeng.com/document/detail/zh/kunpenghpcs/hpckit/devg/kunpengaccel_kml_0189.html
sourcePath: /source/zh/kunpenghpcs/hpckit/devg/kunpengaccel_kml_0189.html
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---
# log10

计算以10为底的对数值。

#### 接口定义

C interface：

float log10f(float x);

double log10(double x);

double log10_18(double x);

long double log10l(long double x);

log10_18仅在高精度版本中提供。


Fortran interface：

RES = LOG10F(X);

RES = LOG10(X);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在log10f中，x是单精度浮点类型。 在log10和log10\_18中，x是双精度浮点类型。 在log10l中，x是长双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |


#### 返回值

- 返回以10为底x的对数函数值y，y ∈ (-INF, +INF)。
- 输入x为±0，返回-∞。
- 输入x为1，返回0。
- 输入x为负数，返回nan。
- 输入x为-∞，返回nan。
- 输入x为+∞，返回+∞。
- 输入x为nan，返回nan。


#### 依赖

C: "km.h"


#### 示例

C interface：```
double pi = acos(-1); 
    // typical usage 
    double x1 = 10.0, x2 = 2.0, x3 = 125, x4 = 5; 
    // special handling 
    double a = 0.0, b = INFINITY, c = -INFINITY, d = NAN, e = 1.0; 
    // print result 
    printf("base-5 logarithm of 125 = %.15f\n", log10(x3)/log10(x4)); 
    printf("log10(1.0) = %.15f\n", log10(e)); 
    printf("log10(10.0) = %.15f\n", log10(x1)); 
    printf("log10(2.0) = %.15f\n", log10(x2)); 
    printf("log10(0.0) = %.15f\n", log10(a)); 
    printf("log10(INFINITY) = %.15f\n", log10(b)); 
    printf("log10(-INFINITY) = %.15f\n", log10(c)); 
    printf("log10(NAN) = %.15f\n", log10(d)); 
    /* 
     *  base-5 logarithm of 125 = 3.000000000000000 
     *  log10(1.0) = 0.000000000000000 
     *  log10(10.0) = 1.000000000000000 
     *  log10(2.0) = 0.301029995663981 
     *  log10(0.0) = -inf 
     *  log10(INFINITY) = inf 
     *  log10(-INFINITY) = nan 
     *  log10(NAN) = nan 
     * 
     * */
```


Fortran interface：

```
REAL(8) :: X = 2
PRINT*,  LOG10(X)
!
! OUTPUT
!     0.301029995663981
!
```