带有范围的 C 中的查找表

Question

我有一个表格，可以根据我需要在 C 中实现的一系列 ADC（模数转换器）计数来计算温度。我不知道该怎么做，因为它不是准确的值，它将在重叠范围内。

代码将接收从传感器读取的 ADC 整数值（第 2-4 列分别表示 ADC 低、ADC 中心和 ADC 高）并输出温度（第 1 列）。这些值来自我从电阻转换为电压到 ADC 的文档。 ADC 值将是一个整数，它需要在该范围内最合适，我认为这意味着最接近中心值。它不需要非常精确，因为它是一个非常稳定的值（通常在 370-350 又名 25-26C 之间），它将用于确定过热 (41C)。

这是表格中几个单元格的示例：

Temperature  | ADC Low     |  ADC Center |  ADC High
-------------+-------------+-------------+------------
          25 | 362.1804923 | 372.3636364 | 382.4913871
          26 | 349.9452011 | 359.9395371 | 369.8908548
          27 | 338.1432261 | 347.9502029 | 357.7197732
          28 | 326.7557813 | 336.3737597 | 345.9668118
          29 | 315.7666703 | 325.2012277 | 334.6164426
          30 | 305.1694416 | 314.4195099 | 323.6592884
          31 | 294.9747625 | 304.0429113 | 313.1063265

任何帮助将不胜感激。

Answer 1

这里有一些可行的代码。它假设映射表是内置的；如果您需要动态阅读它，则需要修改一些代码，但不是基本问题。

如comment 中所述，该代码为每个温度确定一个整数 ADC 值，如果该值大于限制，则温度为给定值，在 ADC 中心值条目之间使用线性插值原始 ADC 数据表。对相关温度的搜索是简单的线性搜索。如果需要，您可以使用二进制搜索，或者创建一个合理的 ADC 值表并将每个 ADC 值映射到温度（使用更多空间，但提供最快的查找）。但是对于 25-41ºC 的范围，几乎不值得担心线性搜索的性能，除非你能证明它是一个严重的瓶颈，特别是因为正常搜索只需要在开始时查看 2 或 3 个条目列表（因此正常的线性搜索可能会胜过二分搜索！）。

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

struct raw_adc
{
    int temp;
    double adc_lo;
    double adc_mid;
    double adc_hi;
};

/* Assumed sorted in order of increasing temperature */
/* Assumed monotonic in order of adc_mid values in sorted order */
/* Assumed lower temperature has higher adc_mid value */
/* Assumed ADC readings always positive (0 used as dummy) */
/* Assume contiguous series of temperatures */
static struct raw_adc raw_adc_data[] =
{
    { 25, 362.1804923, 372.3636364, 382.4913871 },
    { 26, 349.9452011, 359.9395371, 369.8908548 },
    { 27, 338.1432261, 347.9502029, 357.7197732 },
    { 28, 326.7557813, 336.3737597, 345.9668118 },
    { 29, 315.7666703, 325.2012277, 334.6164426 },
    { 30, 305.1694416, 314.4195099, 323.6592884 },
    { 31, 294.9747625, 304.0429113, 313.1063265 },
};
enum { NUM_RAW_ADC = sizeof(raw_adc_data) / sizeof(raw_adc_data[0]) };

struct map_adc
{
    int temp;
    int adc_value;
};

static struct map_adc adc_map[NUM_RAW_ADC];

static void map_raw_adc_values(void)
{
    int i;
    for (i = 0; i < NUM_RAW_ADC - 1; i++)
    {
        adc_map[i].temp = raw_adc_data[i].temp;
        /* Optionally add 0.5 before assigning */
        adc_map[i].adc_value = (raw_adc_data[i].adc_mid + raw_adc_data[i+1].adc_mid) / 2;
    }
    /* Last value is deemed to be hotter than the last recorded value */
    adc_map[i].temp = adc_map[i-1].temp + 1;
    adc_map[i].adc_value = 0;
}

static int temp_from_adc(int adc_value)
{
    int i;
    for (i = 0; i < NUM_RAW_ADC; i++)
    {
        /* Use of > determined by inspection of data - colder temps have higher ADC value */
        if (adc_value > adc_map[i].adc_value)
            return adc_map[i].temp;
    }
    assert(0);      /* Can't happen! */
    return 300;     /* If it gets here, the machine is too hot! */
}

static void dump_adc_map(void)
{
    for (int i = 0; i < NUM_RAW_ADC; i++)
    {
        assert(raw_adc_data[i].temp == adc_map[i].temp);
        printf("T = %.3dºC ADC = (%6.2f:%6.2f:%6.2f) Limit = %d\n",
                raw_adc_data[i].temp, raw_adc_data[i].adc_lo,
                raw_adc_data[i].adc_mid, raw_adc_data[i].adc_hi,
                adc_map[i].adc_value);
    }
}

int main(void)
{
    map_raw_adc_values();
    dump_adc_map();
    srand(time(0));
    for (int i = 0; i < 20; i++)
    {
        /* Range of ADC values in table is 294-382 */
        /* Generate random value in that range */
        int adc_rdg = rand() % (382 - 294) + 294;
        printf("ADC: %d = %d ºC\n", adc_rdg, temp_from_adc(adc_rdg));
    }
    return 0;
}

示例运行：

T = 025ºC ADC = (362.18:372.36:382.49) Limit = 366
T = 026ºC ADC = (349.95:359.94:369.89) Limit = 353
T = 027ºC ADC = (338.14:347.95:357.72) Limit = 342
T = 028ºC ADC = (326.76:336.37:345.97) Limit = 330
T = 029ºC ADC = (315.77:325.20:334.62) Limit = 319
T = 030ºC ADC = (305.17:314.42:323.66) Limit = 309
T = 031ºC ADC = (294.97:304.04:313.11) Limit = 0
ADC: 298 = 31 ºC
ADC: 358 = 26 ºC
ADC: 343 = 27 ºC
ADC: 315 = 30 ºC
ADC: 358 = 26 ºC
ADC: 352 = 27 ºC
ADC: 374 = 25 ºC
ADC: 322 = 29 ºC
ADC: 372 = 25 ºC
ADC: 376 = 25 ºC
ADC: 333 = 28 ºC
ADC: 334 = 28 ºC
ADC: 356 = 26 ºC
ADC: 307 = 31 ºC
ADC: 304 = 31 ºC
ADC: 305 = 31 ºC
ADC: 324 = 29 ºC
ADC: 358 = 26 ºC
ADC: 324 = 29 ºC
ADC: 322 = 29 ºC

Answer 2

我在想：使用二分搜索遍历声明范围的结构数组：

struct Range {
    float low;
    float center;
    float high;
    int   temperature;
};

struct RangeTable {
    struct Range* list;
    size_t length;
}

// TODO: Read the file here

struct RangeTable* table = ...
// NOTE: Ensure table.list is sorted in ascending `center` value, either in the file, or use a sorting function on the array after loading.

/////////////

/// <summary>Looks up the <paramref="adcReading" /> value in the provided table and returns a pointer to the best-matching Range struct value.</summary>
struct Range* lookup( struct RangeTable * table, float adcReading ) {

    // do a binary-search on the `center` value, which will return the Range object with the closest `center` value.
    struct Range* closestCenter = binarySearch( table->list, table->length, adcReading );

    if( closestCenter == NULL ) {
        // error condition.
        exit( 1 );
    }
    if( adcReading < closestCenter->low || adcReading > closestCenter->high ) {
        // out of range
    }
    else {
        // inside the range
    }
}

当然，实现排序和二进制搜索功能取决于您。