Finish converting GSL to absl::Span

One less dependency.

Change-Id: Iaac25a3c1312a21a8a2b77b8cfee2463bdb51196
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/motors/peripheral/BUILD b/motors/peripheral/BUILD
index a42d502..7765ce1 100644
--- a/motors/peripheral/BUILD
+++ b/motors/peripheral/BUILD
@@ -45,7 +45,7 @@
     hdrs = ["uart_buffer.h"],
     visibility = ["//visibility:public"],
     deps = [
-        "//third_party/GSL",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
@@ -72,7 +72,7 @@
         "//aos/containers:sized_array",
         "//motors:util",
         "//motors/core",
-        "//third_party/GSL",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
@@ -99,6 +99,6 @@
         ":uart_buffer",
         "//motors:util",
         "//motors/core",
-        "//third_party/GSL",
+        "@com_google_absl//absl/types:span",
     ],
 )
diff --git a/motors/peripheral/spi.cc b/motors/peripheral/spi.cc
index c0bb767..8c4ad11 100644
--- a/motors/peripheral/spi.cc
+++ b/motors/peripheral/spi.cc
@@ -57,7 +57,7 @@
   spi_.FlushInterruptRequests();
 }
 
-void InterruptBufferedSpi::Write(gsl::span<const char> data,
+void InterruptBufferedSpi::Write(absl::Span<const char> data,
                                  DisableInterrupts *disable_interrupts) {
   frames_to_receive_ += data.size();
   // Until we get all of the data queued, we'll call WriteFrames from our
@@ -82,11 +82,11 @@
   }
 }
 
-gsl::span<char> InterruptBufferedSpi::Read(
-    gsl::span<char> buffer, DisableInterrupts *disable_interrupts) {
+absl::Span<char> InterruptBufferedSpi::Read(
+    absl::Span<char> buffer, DisableInterrupts *disable_interrupts) {
   size_t bytes_read = 0;
   {
-    const gsl::span<const char> read_data =
+    const absl::Span<const char> read_data =
         receive_buffer_.PopSpan(buffer.size());
     std::copy(read_data.begin(), read_data.end(), buffer.begin());
     bytes_read += read_data.size();
@@ -95,7 +95,7 @@
   ReenableInterrupts{disable_interrupts};
 
   {
-    const gsl::span<const char> read_data =
+    const absl::Span<const char> read_data =
         receive_buffer_.PopSpan(buffer.size() - bytes_read);
     std::copy(read_data.begin(), read_data.end(),
               buffer.subspan(bytes_read).begin());
diff --git a/motors/peripheral/spi.h b/motors/peripheral/spi.h
index 1cfb385..5361f91 100644
--- a/motors/peripheral/spi.h
+++ b/motors/peripheral/spi.h
@@ -1,10 +1,10 @@
 #ifndef MOTORS_PERIPHERAL_SPI_H_
 #define MOTORS_PERIPHERAL_SPI_H_
 
+#include "absl/types/span.h"
 #include "motors/core/kinetis.h"
 #include "motors/peripheral/uart_buffer.h"
 #include "motors/util.h"
-#include "third_party/GSL/include/gsl/gsl"
 
 namespace frc971 {
 namespace teensy {
@@ -41,21 +41,11 @@
   }
 
   // Calling code must synchronize all of these.
-  void EnableTransmitInterrupt() {
-    rser_value_ |= M_SPI_TFFF_RE;
-  }
-  void DisableTransmitInterrupt() {
-    rser_value_ &= ~M_SPI_TFFF_RE;
-  }
-  void EnableReceiveInterrupt() {
-    rser_value_ |= M_SPI_RFDF_RE;
-  }
-  void DisableReceiveInterrupt() {
-    rser_value_ &= ~M_SPI_RFDF_RE;
-  }
-  void FlushInterruptRequests() {
-    module_->RSER = rser_value_;
-  }
+  void EnableTransmitInterrupt() { rser_value_ |= M_SPI_TFFF_RE; }
+  void DisableTransmitInterrupt() { rser_value_ &= ~M_SPI_TFFF_RE; }
+  void EnableReceiveInterrupt() { rser_value_ |= M_SPI_RFDF_RE; }
+  void DisableReceiveInterrupt() { rser_value_ &= ~M_SPI_RFDF_RE; }
+  void FlushInterruptRequests() { module_->RSER = rser_value_; }
 
  private:
   KINETISK_SPI_t *const module_;
@@ -88,18 +78,20 @@
 
   // Queues up the given data for immediate writing. Blocks only if the queue
   // fills up before all of data is enqueued.
-  void Write(gsl::span<const char> data, DisableInterrupts *disable_interrupts);
+  void Write(absl::Span<const char> data,
+             DisableInterrupts *disable_interrupts);
 
   // Reads currently available data.
   // Returns all the data which is currently available (possibly none);
   // buffer is where to store the result. The return value will be a subspan of
   // this.
-  gsl::span<char> Read(gsl::span<char> buffer,
-                       DisableInterrupts *disable_interrupts);
+  absl::Span<char> Read(absl::Span<char> buffer,
+                        DisableInterrupts *disable_interrupts);
 
   // Should be called as the body of the interrupt handler.
   void HandleInterrupt(const DisableInterrupts &disable_interrupts) {
-    while (ReadAndWriteFrame(true, disable_interrupts)) {}
+    while (ReadAndWriteFrame(true, disable_interrupts)) {
+    }
     spi_.FlushInterruptRequests();
   }
 
diff --git a/motors/peripheral/uart.cc b/motors/peripheral/uart.cc
index 9cd4014..6e48320 100644
--- a/motors/peripheral/uart.cc
+++ b/motors/peripheral/uart.cc
@@ -52,12 +52,12 @@
   module_->RWFIFO = 1;
 }
 
-void Uart::DoWrite(gsl::span<const char> data) {
+void Uart::DoWrite(absl::Span<const char> data) {
   // In theory, we could be more efficient about this by writing the number of
   // bytes we know there's space for and only calling SpaceAvailable() (or
   // otherwise reading S1) before the final one. In practice, the FIFOs are so
   // short on this part it probably won't help anything.
-  for (int i = 0; i < data.size(); ++i) {
+  for (size_t i = 0; i < data.size(); ++i) {
     while (!SpaceAvailable()) {
     }
     WriteCharacter(data[i]);
@@ -93,7 +93,7 @@
   }
 }
 
-void InterruptBufferedUart::Write(gsl::span<const char> data) {
+void InterruptBufferedUart::Write(absl::Span<const char> data) {
   DisableInterrupts disable_interrupts;
   uart_.EnableTransmitInterrupt(disable_interrupts);
   while (!data.empty()) {
@@ -104,18 +104,18 @@
   }
 }
 
-gsl::span<char> InterruptBufferedUart::Read(gsl::span<char> buffer) {
+absl::Span<char> InterruptBufferedUart::Read(absl::Span<char> buffer) {
   size_t bytes_read = 0;
   {
     DisableInterrupts disable_interrupts;
-    const gsl::span<const char> read_data =
+    const absl::Span<const char> read_data =
         receive_buffer_.PopSpan(buffer.size());
     std::copy(read_data.begin(), read_data.end(), buffer.begin());
     bytes_read += read_data.size();
   }
   {
     DisableInterrupts disable_interrupts;
-    const gsl::span<const char> read_data =
+    const absl::Span<const char> read_data =
         receive_buffer_.PopSpan(buffer.size() - bytes_read);
     std::copy(read_data.begin(), read_data.end(),
               buffer.subspan(bytes_read).begin());
diff --git a/motors/peripheral/uart.h b/motors/peripheral/uart.h
index ffb1529..d51bcfe 100644
--- a/motors/peripheral/uart.h
+++ b/motors/peripheral/uart.h
@@ -1,11 +1,11 @@
 #ifndef MOTORS_PERIPHERAL_UART_H_
 #define MOTORS_PERIPHERAL_UART_H_
 
+#include "absl/types/span.h"
 #include "aos/containers/sized_array.h"
 #include "motors/core/kinetis.h"
 #include "motors/peripheral/uart_buffer.h"
 #include "motors/util.h"
-#include "third_party/GSL/include/gsl/gsl"
 
 namespace frc971 {
 namespace teensy {
@@ -22,7 +22,7 @@
   void Initialize(int baud_rate);
 
   // Blocks until all of the data is at least queued.
-  void Write(gsl::span<const char> data, const DisableInterrupts &) {
+  void Write(absl::Span<const char> data, const DisableInterrupts &) {
     DoWrite(data);
   }
 
@@ -77,7 +77,7 @@
     module_->C2 = c2_value_;
   }
 
-  void DoWrite(gsl::span<const char> data);
+  void DoWrite(absl::Span<const char> data);
   aos::SizedArray<char, 4> DoRead();
 
   KINETISK_UART_t *const module_;
@@ -100,13 +100,13 @@
 
   // Queues up the given data for immediate writing. Blocks only if the queue
   // fills up before all of data is enqueued.
-  void Write(gsl::span<const char> data);
+  void Write(absl::Span<const char> data);
 
   // Reads currently available data.
   // Returns all the data which is currently available (possibly none);
   // buffer is where to store the result. The return value will be a subspan of
   // this.
-  gsl::span<char> Read(gsl::span<char> buffer);
+  absl::Span<char> Read(absl::Span<char> buffer);
 
   // Should be called as the body of the interrupt handler.
   void HandleInterrupt(const DisableInterrupts &disable_interrupts) {
diff --git a/motors/peripheral/uart_buffer.h b/motors/peripheral/uart_buffer.h
index 19015bb..c324a2d 100644
--- a/motors/peripheral/uart_buffer.h
+++ b/motors/peripheral/uart_buffer.h
@@ -2,8 +2,9 @@
 #define MOTORS_PERIPHERAL_UART_BUFFER_H_
 
 #include <array>
+#include <cstring>
 
-#include "third_party/GSL/include/gsl/gsl"
+#include "absl/types/span.h"
 
 namespace frc971 {
 namespace teensy {
@@ -13,14 +14,14 @@
 class UartBuffer {
  public:
   // Returns the number of characters added.
-  __attribute__((warn_unused_result)) int PushSpan(gsl::span<const char> data);
+  __attribute__((warn_unused_result)) int PushSpan(absl::Span<const char> data);
 
   // max is the maximum size the returned span should be.
   // The data in the result is only valid until another method is called.
   // Note that this may not return all available data when doing so would
   // require wrapping around, but it will always return a non-empty span if any
   // data is available.
-  gsl::span<const char> PopSpan(int max);
+  absl::Span<const char> PopSpan(int max);
 
   bool empty() const { return size_ == 0; }
   bool full() const { return size_ == kSize; }
@@ -44,7 +45,7 @@
 };
 
 template <int kSize>
-int UartBuffer<kSize>::PushSpan(gsl::span<const char> data) {
+int UartBuffer<kSize>::PushSpan(absl::Span<const char> data) {
   const int end_location = (start_ + size_) % kSize;
   const int remaining_end = ::std::min(kSize - size_, kSize - end_location);
   const int on_end = ::std::min<int>(data.size(), remaining_end);
@@ -65,9 +66,10 @@
 }
 
 template <int kSize>
-gsl::span<const char> UartBuffer<kSize>::PopSpan(int max) {
+absl::Span<const char> UartBuffer<kSize>::PopSpan(int max) {
   const size_t result_size = std::min(max, std::min(kSize - start_, size_));
-  const auto result = gsl::span<const char>(data_).subspan(start_, result_size);
+  const auto result =
+      absl::Span<const char>(data_).subspan(start_, result_size);
   start_ = (start_ + result_size) % kSize;
   size_ -= result_size;
   return result;