hameg-hmo: Replace floating point comparison for vdiv

This should fix bug #731.

diff --git a/src/hardware/hameg-hmo/protocol.c b/src/hardware/hameg-hmo/protocol.c
index 89825b7343592a6e1e7b1388ff5c4efbaac49c88..bcf68ebb7ce1dda9316c7a17271c553cea2e96c8 100644 (file)
--- a/src/hardware/hameg-hmo/protocol.c
+++ b/src/hardware/hameg-hmo/protocol.c
@@ -327,13 +327,75 @@ static int scope_state_get_array_option(struct sr_scpi_dev_inst *scpi,
        return SR_OK;
 }
 
+/**
+ * This function takes a value of the form "2.000E-03", converts it to a
+ * significand / factor pair and returns the index of an array where
+ * a matching pair was found.
+ *
+ * It's a bit convoluted because of floating-point issues. The value "10.00E-09"
+ * is parsed by g_ascii_strtod() as 0.000000009999999939, for example.
+ * Therefore it's easier to break the number up into two strings and handle
+ * them separately.
+ *
+ * @param value The string to be parsed.
+ * @param array The array of s/f pairs.
+ * @param array_len The number of pairs in the array.
+ * @param result The index at which a matching pair was found.
+ *
+ * @return SR_ERR on any parsing error, SR_OK otherwise.
+ */
+static int array_float_get(gchar *value, const uint64_t array[][2],
+               int array_len, int *result)
+{
+       int i;
+       uint64_t f;
+       float s;
+       unsigned int s_int;
+       gchar ss[10], es[10];
+
+       memset(ss, 0, sizeof(ss));
+       memset(es, 0, sizeof(es));
+
+       strncpy(ss, value, 5);
+       strncpy(es, &(value[6]), 3);
+
+       if (sr_atof_ascii(ss, &s) != SR_OK)
+               return SR_ERR;
+       if (sr_atoi(es, &i) != SR_OK)
+               return SR_ERR;
+
+       /* Transform e.g. 10^-03 to 1000 as the array stores the inverse. */
+       f = pow(10, abs(i));
+
+       /*
+        * Adjust the significand/factor pair to make sure
+        * that f is a multiple of 1000.
+        */
+       while ((int)fmod(log10(f), 3) > 0) {
+               s *= 10;
+               f *= 10;
+       }
+
+       /* Truncate s to circumvent rounding errors. */
+       s_int = (unsigned int)s;
+
+       for (i = 0; i < array_len; i++) {
+               if ((s_int == array[i][0]) && (f == array[i][1])) {
+                       *result = i;
+                       return SR_OK;
+               }
+       }
+
+       return SR_ERR;
+}
+
 static int analog_channel_state_get(struct sr_scpi_dev_inst *scpi,
                                    const struct scope_config *config,
                                    struct scope_state *state)
 {
        unsigned int i, j;
-       float tmp_float;
        char command[MAX_COMMAND_SIZE];
+       char *tmp_str;
 
        for (i = 0; i < config->analog_channels; i++) {
                g_snprintf(command, sizeof(command),
@@ -348,20 +410,19 @@ static int analog_channel_state_get(struct sr_scpi_dev_inst *scpi,
                           (*config->scpi_dialect)[SCPI_CMD_GET_VERTICAL_DIV],
                           i + 1);
 
-               if (sr_scpi_get_float(scpi, command, &tmp_float) != SR_OK)
+               if (sr_scpi_get_string(scpi, command, &tmp_str) != SR_OK)
                        return SR_ERR;
-               for (j = 0; j < config->num_vdivs; j++) {
-                       if (tmp_float == ((float) (*config->vdivs)[j][0] /
-                                         (*config->vdivs)[j][1])) {
-                               state->analog_channels[i].vdiv = j;
-                               break;
-                       }
-               }
-               if (j == config->num_vdivs) {
+
+               if (array_float_get(tmp_str, hmo_vdivs, ARRAY_SIZE(hmo_vdivs),
+                               &j) != SR_OK) {
+                       g_free(tmp_str);
                        sr_err("Could not determine array index for vertical div scale.");
                        return SR_ERR;
                }
 
+               g_free(tmp_str);
+               state->analog_channels[i].vdiv = j;
+
                g_snprintf(command, sizeof(command),
                           (*config->scpi_dialect)[SCPI_CMD_GET_VERTICAL_OFFSET],
                           i + 1);