diff --git a/liba/Makefile b/liba/Makefile
index 0a3962929..c860db2a0 100644
--- a/liba/Makefile
+++ b/liba/Makefile
@@ -2,7 +2,20 @@ SFLAGS += -Iliba/include
 
 liba/src/external/sqlite/mem5.o: CFLAGS += -w
 
-objs += $(addprefix liba/src/, assert.o errno.o malloc.o memcpy.o memset.o strcmp.o strlcpy.o strlen.o external/sqlite/mem5.o)
+objs += $(addprefix liba/src/, \
+  assert.o \
+  errno.o \
+  ieee754.o \
+  isnanf.o \
+  isinff.o \
+  malloc.o \
+  memcpy.o \
+  memset.o \
+  strcmp.o \
+  strlcpy.o \
+  strlen.o \
+  external/sqlite/mem5.o \
+)
 
 objs += $(addprefix liba/src/external/openbsd/, \
   e_log10f.o \
@@ -25,7 +38,11 @@ objs += $(addprefix liba/src/external/openbsd/, \
 
 liba/src/external/openbsd/%.o: CFLAGS += -Iliba/src/external/openbsd/include -Wno-parentheses
 
-tests += $(addprefix liba/test/, stdint.c strlcpy.c)
+tests += $(addprefix liba/test/, \
+  ieee754.c \
+  stdint.c \
+  strlcpy.c \
+)
 
 # The use of aeabi-rt could be made conditional to an AEABI target.
 # In practice we're always using liba on such a target.
diff --git a/liba/include/math.h b/liba/include/math.h
index 7ec64c08a..235eb252e 100644
--- a/liba/include/math.h
+++ b/liba/include/math.h
@@ -5,6 +5,9 @@
 
 LIBA_BEGIN_DECLS
 
+int isinff(float x);
+int isnanf(float x);
+
 float copysignf(float x, float y);
 float cosf(float x);
 float fabsf(float x);
diff --git a/liba/include/private/ieee754.h b/liba/include/private/ieee754.h
new file mode 100644
index 000000000..e8e567266
--- /dev/null
+++ b/liba/include/private/ieee754.h
@@ -0,0 +1,9 @@
+#ifndef LIBA_IEEE754_H
+#define LIBA_IEEE754_H
+
+#include <stdint.h>
+
+uint32_t ieee754man(float x);
+uint8_t ieee754exp(float x);
+
+#endif
diff --git a/liba/src/ieee754.c b/liba/src/ieee754.c
new file mode 100644
index 000000000..a7904f474
--- /dev/null
+++ b/liba/src/ieee754.c
@@ -0,0 +1,19 @@
+#include <private/ieee754.h>
+
+uint32_t ieee754man(float x) {
+  union {
+    float f;
+    uint32_t i;
+  } u;
+  u.f = x;
+  return (u.i & ((1<<23)-1));
+}
+
+uint8_t ieee754exp(float x) {
+  union {
+    float f;
+    uint32_t i;
+  } u;
+  u.f = x;
+  return (u.i >> 23) & 0xFF;
+}
diff --git a/liba/src/isinff.c b/liba/src/isinff.c
new file mode 100644
index 000000000..f184f2252
--- /dev/null
+++ b/liba/src/isinff.c
@@ -0,0 +1,6 @@
+#include <math.h>
+#include <private/ieee754.h>
+
+int isinff(float x) {
+  return (ieee754exp(x) == 0xFF && ieee754man(x) == 0);
+}
diff --git a/liba/src/isnanf.c b/liba/src/isnanf.c
new file mode 100644
index 000000000..97eb74cec
--- /dev/null
+++ b/liba/src/isnanf.c
@@ -0,0 +1,6 @@
+#include <math.h>
+#include <private/ieee754.h>
+
+int isnanf(float x) {
+  return (ieee754exp(x) == 0xFF && ieee754man(x) != 0);
+}
diff --git a/liba/test/ieee754.c b/liba/test/ieee754.c
new file mode 100644
index 000000000..c59875ac5
--- /dev/null
+++ b/liba/test/ieee754.c
@@ -0,0 +1,12 @@
+#include <quiz.h>
+#include <assert.h>
+#include <private/ieee754.h>
+
+QUIZ_CASE(liba_ieee754) {
+  assert(ieee754man(123.456f) == 7793017);
+  assert(ieee754exp(123.456f) == 133);
+  assert(ieee754man(555.555f) == 713605);
+  assert(ieee754exp(555.555f) == 136);
+  assert(ieee754man(0.007f) == 6643778);
+  assert(ieee754exp(0.007f) == 119);
+}